Forest and Shade Trees of Iowa (Bur Oak Guide) [3 ed.] 1587299941, 9781587299940

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Forest and Shade Trees of Iowa T h i r d E di t ion

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Forest and Shade Trees of Iowa T h i r d E di t ion

Peter J. van der Linden and Donald R. Farrar

University of  Iowa Press, Iowa City A Bu r Oa k Gu i de

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University of Iowa Press, Iowa City 52242 Copyright © 2011 by the University of Iowa Press www.uiowapress.org Printed in China Design by April Leidig-Higgins No part of this book may be reproduced or used in any form or by any means without permission in writing from the publisher. All reasonable steps have been taken to contact copyright holders of material used in this book. The publisher would be pleased to make suitable arrangements with any whom it has not been possible to reach. The University of Iowa Press is a member of Green Press Initiative and is committed to preserving natural resources. Printed on acid-free paper Library of Congress Cataloging-in-Publication Data Van der Linden, Peter J., 1953– Forest and shade trees of Iowa / by Peter J. van der Linden and Donald R. Farrar. — 3rd ed. p.  cm.—(A Bur Oak guide) Includes bibliographical references and index. ISBN-13: 978-1-58729-994-0, ISBN-10: 1-58729-994-1 (pbk.) ISBN-13: 978-1-58729-995-7, ISBN-10: 1-58729-995-X (e-book) 1. Trees — Iowa — Identification.  2. Shade trees —  Iowa — Identification.  I. Farrar, Donald R., 1941–  II. Title.  III. Series: Bur Oak guide. QK160.V36  2011   2010049211 582.1609777 — dc22 With the exception of photos on pages vi, 290, and 292, by Peter van der Linden, page 349 (top) by Mark and John van der Linden, and page 357 by Judy van der Linden, all photos are by Donald Farrar.

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Contents Acknowledgments  vii About the Photographs  ix Introduction to the Third Edition  xi

1 Identifying Iowa’s Trees  1 Identifying Trees  3 Summer Keys to Iowa’s Trees  15 Winter Keys to Iowa’s Trees  41 Descriptions of  Tree Species  57

2 The Natural History and Uses of  Iowa’s Trees  265 Conifers  267 Flowering Trees  285 Promising Trees for Iowa  379

3 Growing Trees in Iowa  383 4 Iowa’s Forests  399 5 Good Places to See Trees in Iowa  409 Glossary  415 Bibliography  419 Index  427

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Acknowledgments W e a r e especi a lly thankful for the inspirational work of the late botanist and artist Anna Gardner. Her pioneering use of digital scanning to capture tree characteristics in intimate detail helped thousands of dendrology students become better biologists and provided the basic plan for the plates in this book. Many of Anna’s original, beautifully informative scanned images are included in this book. We are deeply indebted to Chanda Skelton for contributing her artistic, botanical, and computer skills to the construction of the plates from thousands of potential images and for managing the huge image database. We are grateful to Jeffery Iles, professor and chair in the Department of Horticulture at Iowa State University, for contributing his recommendations of the best crabapples for Iowa. We thank the Iowa State University Publication Endowment Fund for funding in support of this project. Finally, we acknowledge the artistry of Carol Jacobs, who created the drawings that appeared in all three editions of this book.

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About the Photographs Tr ees provide endless fascination as photographic subjects. The form, color, texture, and intricate patterns of their leaves, flowers, fruits, branches, and trunks lend themselves well to artistic expression as well as relevance to species identification and ecological function. The images in this book were captured in several ways. In the plates accompanying the species descriptions, the full-page background images of leafy branches were made with a flatbed scanner, Epson Perfection 3200, using freshly collected material. Images of other twodimensional subjects such as leaf scars were also made in this way. Threedimensional images such as flowers, fruits, and bark were photographed with a Canon PowerShot G9 digital camera. To enhance the clarity of some subjects such as fruits and bark, a monochrome background was produced digitally in Adobe Photoshop. The color, form, and texture of the plants are natural, modified only through increased brightness of some underexposed images. Surface texture of single leaves in fall color was enhanced through use of  lowangle lighting. The photos in part 2 were made with the Canon G9 digital camera and by digitally scanning older slide photos made with a Pentax K1000 camera using a 50mm macro lens and Ektachrome 64 or 120 film. Readers will recognize the locations of many of these photos, as they were taken at public institutions or popular parks in Iowa. Others were taken in neighboring states but show typical Iowa scenes. It is impossible to ignore the ambience of trees in Iowa. We hope that all of these images will contribute to the reader’s enjoyment of their many blessings.

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Introduction to the Third Edition This book is a guide to Iowa’s trees, both native and introduced. Readers of our first two editions will find this one looks much different, with color photos and the information organized in a new way. There are two main parts, dealing separately with tree identification and the natural history and uses of trees. Following these are shorter chapters describing the planting and care of trees, Iowa’s forests, and good places to see trees in Iowa. We hope that both new and long-time users of the book will find this organization helpful. Part 1 focuses on identification. It includes an introduction to tree identification, keys to trees in both summer and winter, and descriptions and photographs of common trees. To facilitate identification by readers who are not experts in botany, the species are arranged according to similarities in foliage. Thus, walnuts and locusts are grouped in the same section because they both have alternate compound leaves, even though they are not closely related. Measurements are in English, not metric units, because most users of the book will be more familiar with the former. Part 2 contains discussions about individual trees — how and where they grow and how they can be used. This part of the book is more comprehensive, including all trees native to Iowa, some less commonly planted trees, and tall native shrubs. The trees are divided into two sections; conifers are discussed first, then flowering trees. Since there is no obvious or best way to organize the species within each section, we have arranged them in a sequence that will at least be familiar to some readers — in alphabetical order by genus name. If you don’t know the genus name, look for the tree’s common name in the index. The nomenclature of plants can be confusing, but fortunately the common names of most trees have become standardized over the years. Where more than one name is in common use, we include the alternate names in the text. Botanical names in most cases follow Eilers and Roosa (1994); other sources are listed in the bibliography. Important synonyms are included for reference. We are all influenced by our education and life experiences. When recommending trees and discussing their relative values, it is inevitable that the writers’ opinions will come into play. The authors have based their suggestions on long experience, but we realize that others who work with trees may differ.

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xii i n t r o d u c t i o n t o t h e t h i r d e d i t i o n We would not discourage any reader from consulting with arborists, foresters, horticulturists, and other experts in their community or from following their advice if it is contrary to ours. We note cultivars for some species, but this is more for informational purposes than as suggestions for planting. We do not make cultivar recommendations for two reasons. First, the relative merits of different cultivars are to some extent a matter of opinion, and since we lack expertise in this area, we do not wish to take sides. Second, most cultivars are clones, and if widely planted, they would create a community forest with very low genetic variability. We encourage Iowans to plant as diverse a population of trees as possible. Crabapples are a notable exception, because most of the available trees are cultivars, and readers may need some guidance in selecting among the many choices they have. To keep this book current for as long as possible, we have omitted information that can quickly become obsolete, for example, the best pesticides to use in treating particular problems. Readers will find their county extension office and local garden centers to be good sources of information not included here. Since the second edition of this book was published, the Internet has become an important tool for finding information in most disciplines. In some places we refer readers to specific websites that can be helpful, for example, Iowa State University and the Iowa Department of Natural Resources. Because websites can be discontinued or reorganized, we have omitted URLs for individual pages in most cases. We trust that readers can follow the links once connected to a site’s home page. Finally, this book is designed for a general audience, not a scientific one. To avoid cluttering the manuscript with citations, most sources are not identified. Those cited in the text or used as references are included in a bibliography at the end of the book. If you do not know the meaning of a term used in the descriptions, see the glossary. We hope this book leads to a greater understanding and appreciation of Iowa’s trees. We welcome comments from readers as to how it may be improved in the future.

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part one

Identifying Iowa’s Trees

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Identifying Trees You a r e wa lk ing through a park in your community and discover a tree you haven’t seen before. How do you identify it? One way is to compare your tree with the photos in this book, checking page by page until you find a match. To make your search easier, we have arranged the trees in groups based upon similarities in leaves. To get started, go to page 57 and select the appropriate group. When you think you’ve found the right species, be sure to read the entire description on that page. Verify that the buds, fruits, and other features of your tree match that species, too. Some less common species are not illustrated in this book, so you might not find them using the above approach. In that event, we suggest that you use the keys beginning on page 16. If you haven’t used a key before, don’t be afraid to try. Think of it as a scavenger hunt, in which a series of clues helps you find the identity of your tree, one step at a time. Each clue consists of two descriptions, one that matches your tree and one that doesn’t. When you have decided which description is the right one, the key refers you to the next clue, and the search continues. If the above methods don’t work, consult a local expert. Most colleges, arboretums, and garden centers employ people who are skilled in plant identification. You can also take a sample to your county extension office, which will send it to Iowa State University. Each sample should be a branch 6 to 10 inches long with several leaves, plus fruits or seeds if they are available.

Names of  Trees Trees have both common names and botanical names. Most people prefer the common names because they are easy to spell, pronounce, and remember. Botanical names, which are based on Greek and Latin words, are intimidating to many people. They do have an advantage, though, in being standardized by international convention and thus more precise. For example, there are two small trees in the birch family that grow together in woodlands across much of Iowa. One is called ironwood or hop hornbeam; the other is variously known as ironwood, hornbeam, bluebeech,

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4 i d e n t i f y i n g i o w a ’ s t r e e s or musclewood. If someone uses the name ironwood or hornbeam, which tree do they mean? There is no question if they use the botanical name — Ostrya virginiana for the first and Carpinus caroliniana for the second. Another advantage of botanical names is that they are based on natural relationships. The common names green ash, mountain-ash, and prickly-ash all contain the word “ash,” but these species only superficially resemble one another and actually belong to different botanical families. Only the first is a true ash. Similarly, Russian-olive is not an olive, Douglas-fir is not a fir, and Kentucky coffee tree is unrelated to the coffee of commerce. Conversely, poplars, aspens, and cottonwood share many features and are closely related, but their common names do not indicate any relationship. Botanical names have two parts, each of which tells us something about the tree. The first part indicates the genus (plural, genera), or group of related species, to which the tree belongs. The second part, called the specific epithet, designates the particular species. For example, Quercus macrocarpa and Quercus rubra are the names of two trees we commonly call bur oak and red oak. Because the first part of their names is identical, we know they belong to the same genus. The second part of their names is different, however, so we know they are distinct species. The specific epithet usually indicates something about the nature of the tree. For example, macrocarpa means “big fruit” and refers to the large acorn typical of the bur oak and its burlike cup; rubra means red and refers to the reddish color of red oak wood compared to that of white oak. When the botanical names of trees are written, the genus is always capitalized but the specific epithet is not, even when taken from a proper name. Both parts of the name are italicized or underlined. The specific epithet may be followed by the abbreviated surname of the botanist who originally described the species. The “L.” following so many botanical names stands for Carl Linnaeus, a Swedish scientist who designed the modern system of biological nomenclature and described many species. Some species have been subdivided into varieties. The variety name, when indicated, follows the specific epithet. It is underlined or italicized in print but not capitalized. The abbreviation “var.” sometimes precedes it. For example, Quercus macrocarpa var. macrocarpa is the typical variety of bur oak, while var. depressa comprises smaller trees with smaller acorns found in drier areas in the northwest part of the range. As with most varieties within species, where these two varieties grow together they freely hybridize to produce a gradient of tree and acorn sizes.

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Within a species or variety, it is often desirable to distinguish a tree that has been bred or selected for horticultural purposes. For example, ‘Marshall’s Seedless’ is a special type of green ash, selected because it produces no seeds and has attractive dark green leaves. Such selections are called cultivars to distinguish them from naturally occurring varieties. Note that cultivar names are not italicized but instead are capitalized and enclosed by single quotes. Many but not all cultivars are clones. This means that they originated from a single parent tree and are propagated by cuttings, grafting, or other vegetative means to ensure that each tree is a genetic replica of the original.

Features Used for Identification Most people make a leaf collection in school when they are young and through this learn that trees can be identified by differences in their foliage. Other parts of trees are useful for identification, too, including twigs, flowers, fruits, bark, and silhouette. Indeed, it is quite possible to identify trees in winter when leaves are absent. Characteristics of these various tree parts are described below.

Leaves During most of the growing season, leaves are the most conspicuous features of trees. Figure 1 illustrates leaf characteristics. The leaves of most species are remarkably consistent, but variation can occur between individual trees or even on a single tree. The oaks are a notorious example, and species within this genus sometimes cannot be identified without examining buds and fruits in addition to leaves. Leaves for study should be selected from healthy, typical twigs when possible. Leaves from stump or root sprouts (suckers) should be avoided because they can be unusually large and atypically shaped. Lea f Composition A leaf consists of two parts: a broad, flattened portion called the blade and a narrow stalk or petiole. The leaves of most trees, including such familiar types as the oaks and maples, have a single blade. These leaves are said to be simple. Other species have leaves composed of many separate blades or leaflets and are called compound. Ashes and walnuts are two familiar examples. If the leaflets of a compound leaf are arranged along two sides of a central

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leaf compositions

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simple

once-pinnately compound

twice-pinnately compound

leaf arrangement



palmately compound



closely distantly entire toothed toothed

leaf margins opposite

alternate

leaf shapes





linear

lanceolate

Fig. 1. Leaf characteristics.

ovate

obovate

elliptic

oval

oblong

lobed

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axis, like the barbs of a feather, the leaf is once-pinnately compound. If the axis is branched, with leaflets along each branch, the leaf is twice-pinnately compound. A few trees have leaflets radiating from a single point, like the fingers of a hand. These are palmately compound leaves. The composition of a leaf should be the first characteristic noted when you are identifying a tree. Do not confuse the leaflet of a compound leaf with a simple leaf or vice versa, a mistake easily made in spring when the new twigs are green and succulent. How do you tell the difference? Remember that a bud occurs in the angle formed by the twig and each petiole, but not in the angle formed by the axis of a compound leaf and each leaflet. Lea f A r r a ngement The spot on a twig where a leaf is attached is called a node. Most trees have only one leaf per node, an arrangement called alternate. Others are opposite, with two leaves at each node, one on either side of the twig. One Iowa tree, the catalpa, is whorled with three leaves at most nodes. Lea f Sh a pe The outline or shape of leaves varies among species but is usually consistent within a species. Some of the more common shapes are illustrated in figure 1. Leaves with large indentations are said to be lobed. The projecting portions of the blades are called lobes and the spaces between the lobes are known as sinuses. Lea f M a rgins The margins or edges of leaves often have tiny points called teeth. When the teeth are close together, the margin is closely toothed; when they are widely spaced, the margin is distantly toothed. An unbroken leaf margin is said to be entire. Lea f Sur faces The upper surfaces of some leaves are noticeably glossy or shiny, while the leaves of other species are quite dull. A leaf surface may also be more or less covered with tiny hairlike projections, in which case it is called hairy or pubescent. A leaf with no hairs is glabrous. Lea f A pices a nd Bases The tip or apex (plural, apices) of a leaf may be blunt, rounded, pointed (acute), or tapered to a slender tip (acuminate). Its base may be rounded, heart-shaped, wedge-shaped, or squared-off (truncate).

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Winter Twigs Identifying trees might seem hopeless in winter, when no leaves are present. Fortunately, the winter twigs of most trees are as distinctive as their leaves, so no one need give up identification when the branches are bare. Figure 2 illustrates twig characteristics. Lea f Sca r s When the leaf of a deciduous tree falls in autumn, its petiole leaves a mark on the twig called a leaf scar. The leaf scars of most trees are small and somewhat semicircular, but in some species they are quite large and distinctively shaped. Each leaf scar encloses one or more small dots called bundle scars that mark the spots where the vascular bundles or veins of the leaf entered the twig. Figure 2 illustrates leaf scar shapes. Because leaf scars mark the positions of leaves, they are likewise arranged in one of three ways: alternate if solitary at the nodes, opposite if in pairs, and whorled if in threes. Compound leaves often have large leaf scars with many false terminal bud terminal bud

twig scar

lateral bud

bud scale lateral bud



globose subglobose

bundle scar

Fig. 2. Twig characteristics, bud shapes, and leaf scar shapes.

linear

crescent

V-shaped

round

half-round

continuous pith

heart

chambered pith

elongate

bud shapes

leaf scar

shield

leaf scar

ovoid

U-shaped

bundle scar

ring



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leaf scar shapes

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bundle scars, while simple leaves have small leaf scars with one to three bundle scars, but there are exceptions. Buds A bud is a tiny new twig, waiting for the right conditions to grow. Buds begin to develop early in the growing season and are fully formed by late summer, then remain dormant through the fall and winter. When spring comes, leaves and flowers may come from the same or different buds, depending on the species. Figure 2 illustrates bud shapes. Most buds are covered with one or more scales that protect the delicate tissues within from damage and drying out during winter. The buds of poison ivy and a few small, uncommon trees lack scales and are said to be naked. Naked buds are often protected by a dense covering of hairs. In some tree species, a bud called the terminal bud forms at the tip of each twig. This bud, which limits elongation for the remainder of the growing season, is usually much larger than the lateral buds growing farther down the twig at each node. Other species do not produce terminal buds, although their twig tips usually die back to a lateral bud sometime during the growing season, leaving it in a terminal position. This bud, which is called a false terminal bud, can be recognized as a lateral bud by its size and shape. Look also for a stub or twig scar at its base or side, marking the place where the twig tip died back. (Like other lateral buds, a false terminal bud will have a leaf scar at its base. The twig scar may resemble this in size and shape but will be on the opposite side of the twig and will not have bundle scars.) Stipule Sca r s Stipules are small leaflike structures that occur in pairs on the petioles or twigs of many trees. Those attached to the twig leave two small horizontal lines when they fall, one on either side of the leaf scar. Sometimes one of these will be more prominent than the other. In a few species, they form a line that encircles the twig at each node. Pith The center or core of the twig is called the pith. Often it is narrow and pale in color, resembling the wood, but in some species it is very thick and colorful. When the twig is viewed in cross section, the pith varies from round to angled to star-shaped, depending on the species.

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10 i d e n t i f y i n g i o w a ’ s t r e e s A cut made lengthwise through the center of the twig exposes the pith in longitudinal section. When viewed in this way, the pith of most trees is continuous, forming a solid strand of tissue. If the solid tissue is interrupted by cross walls, the pith is called diaphragmed. If there are cross walls separated by empty space, the pith is called chambered. Other T w ig Featur es The word “thorn” is often used for any sharp, woody structure, but in botany it has a special meaning. True thorns are modified twigs with smooth, often glossy surfaces and no buds or leaf scars. A few trees have short, pointed twigs resembling thorns, but these have buds and/or leaf scars like ordinary twigs. Spines are stipules that are sharply pointed and woody. They occur in pairs, one on either side of each leaf scar. A spur shoot is a short, stubby twig that grows only a fraction of an inch each year. Its outer surface is covered with closely packed leaf scars, and there is a terminal bud at its tip. Spur shoots can appear in many species but are characteristic of only a few, including the apples, crabapples, birches, and ginkgo. The catkin is a special type of flower cluster found in many trees (see the following section). In a few species, the catkins for next year are visible on the twigs during fall and winter, as buds are. They resemble tiny sausages covered with minute, overlapping scales. The color of twigs is often distinctive. The colors noted in the keys and descriptions of this book are for typical twigs during winter. There is natural variation within species and even from season to season in the same tree, as reflected in the photographs.

Flowers All broadleaf trees produce flowers. Most of our larger trees have small greenish blooms that appear before the leaves in spring and are thus easily overlooked. Such flowers are pollinated by wind and have no need for the colorful petals that characterize apples, redbuds, and other small trees. Pines and similar trees are also pollinated by wind, but their reproductive parts occur in cones, not flowers. Tree flowers are distinctive when present, but their usefulness as a means of identification is limited by their short longevity. One reason that willows, haw-

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thorns, and serviceberries are so difficult to identify is that flowers are often needed to differentiate species, and these trees bloom for only a week or two in spring! Tree flowers are not described in detail in this book unless they are necessary to distinguish otherwise similar species. Observing them is an interesting pastime in spring, however, and there are many books that describe their features in more detail. Flow er Pa rts There are four principal flower parts. These, in order from the outside to the center, are the sepals, petals, stamens, and carpels. One or more of these is often absent from small, wind-pollinated flowers. Sepals and petals are leaflike in structure. Sepals are usually green and petals some other color, but sometimes they are colored alike. The sepals are collectively known as the calyx and the petals as the corolla. Flowers without petals are said to be apetalous. Stamens produce pollen and the carpels eventually become fruit. Stamens consist of a stalk or filament and a pollen-bearing sac called the anther. The carpels can be separate from one another or united into a flask-shaped structure called the pistil. Most pistils have a bulbous basal part called the ovary, a neck or style, and a swollen tip called the stigma. If the other flower parts appear to arise from the top of the ovary, the ovary is called inferior. If they arise from the base, the ovary is superior. Flow er Gender A flower containing both stamens and carpels is called perfect or bisexual. One bearing either stamens or carpels but not both is imperfect or unisexual. Each imperfect flower is thus either male or female. Monoecious species have male and female flowers on the same tree. If the two occur on separate trees, so individual trees are either male or female, the tree is dioecious. A species having both perfect and imperfect flowers on the same tree is called polygamous. A r r a ngement of Flow er s A cluster of flowers is called an inflorescence. See figure 3 for inflorescence types. The catkin is a special type of spike found in some wind-pollinated trees. It consists of many tiny, imperfect, apetalous flowers crowded on a stem, forming

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raceme spike



umbel panicle



corymb

Fig. 3. Types of inflorescences.

a long, slender, often drooping inflorescence resembling a cat’s tail. Catkins elongate in the spring, often before the leaves appear, and are usually unisexual.

Fruits A fruit is the ripened, seed-bearing ovary of a flower. Fruits can be large or small, dry or fleshy, with one to many seeds. Botanically speaking, a kernel of corn, a green bean, a walnut, and a sunflower “seed” are all fruits. Fruits are very useful for identification, and in some of the larger genera they are indispensable in distinguishing species. The same is true for the cones of pines, spruces, firs, and related trees, which serve the same function as fruits. Dry Fruits Some dry fruits are podlike, containing several seeds and usually splitting open at maturity. The follicle has a single chamber inside and splits open along one seam, like a milkweed pod. The legume is beanlike, also with one chamber, but has a pair of seams, although it may split open along only one. The capsule, which is derived from an ovary with two or more carpels, usually has two or more seams and at least two internal chambers. Other dry fruits are single-seeded and do not split open. Achenes are very

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small and often have long, silky hairs or prickly hooks to aid in dispersal. Sam­ aras are similar but usually larger, with thin wings that catch the wind. Nuts are relatively large with hard shells and usually a surrounding husk or cup. Small nutlike fruits are called nutlets. Fleshy Fruits The drupe or stone fruit has a single seed with a thick, bony covering, surrounded by a juicy or mealy flesh. Olive, cherries, and peaches are familiar examples. The berry is fleshy throughout with several seeds, as in a grape or a tomato. The pome can be berrylike in appearance but differs in having the seeds confined to the center of the fruit with a thin, cartilaginous wall separating them from the outer pulp. Pomes are derived from an inferior ovary, so the remnants of the calyx can often be seen at the end of the fruit opposite the stem. Apples and pears are pomes.

Bark The bark of trees differs among species, but these differences may be less obvious than differences in leaves, twigs, and fruits. With patience and persistence, though, one can learn to identify most trees in this way. This knowledge can be indispensable when identifying tall trees in the woods, where foliage and twigs are out of reach. Smooth bark is tight-fitting and nearly unbroken. Most species have smooth bark when young, but only a few trees retain it as they mature. Furrowed bark is the most common. It is composed of ridges alternating with valleys or furrows, much like a three-dimensional map of a mountain range. Species can be distinguished by the color of the bark, depth and width of the furrows, width and length of ridges, and the pattern. Scaly bark is broken into small, thin, loosely attached pieces with upturned edges. Platy bark is broken into small, roughly rectangular pieces that are usually appressed to the trunk and more or less arranged in rows. Shaggy bark consists of elongate, irregularly shaped pieces that curve upward at one or both ends, giving the trunk a shaggy appearance. Warty bark is characteristic of the hackberry. It consists of small, warty outgrowths on a smooth background. Eventually the bark of hackberry may become platy.

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columnar

round

pyramidal

oval



oblong

vase-shaped

irregular or asymmetric

Fig. 4. Silhouette types.

Silhouette Trees develop distinctive silhouettes when grown in the open and not crowded by other trees. See figure 4 for silhouette types.

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Summer Keys to Iowa’s Trees The follow ing k ey includes all trees native to Iowa, except for a few uncommon species of hawthorns, and those introduced trees important in landscaping and conservation. Large native and naturalized shrubs that might be mistaken for tree saplings have also been included. When a genus has only one or two species in Iowa, those species are included in the main body of the key; genera with more than two species — maples, serviceberries, birches, hickories, dogwoods, hawthorns, ashes, magnolias, spruces, pines, poplars, cherries and plums, oaks, sumacs, willows, and elms — are keyed in separate sections at the end. Apples and crabapples, pears, lilacs, yews, honeysuckles, and most junipers are keyed to genus only because identification of the many cultivated types is very difficult for nonspecialists. The key is based primarily on characteristics of fully developed leaves, but it includes fruit, twig, flower, and bark characteristics where necessary for accurate identification. Technical terms used in the key are defined in the glossary. To use the key, read the two descriptions numbered “1” and decide which best describes the tree you want to identify. This will refer you to another two descriptions, where you will again select the one that matches your tree. Proceed in this way, step by step, until you determine the identity of your tree.

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General Key

a

b

fig. 6

a

b

c

fig. 5

1. Leaves needlelike or scale-like (fig. 5a, b), usually evergreen: 2 1. Leaves broad and flat with branching veins (fig. 5c), deciduous in autumn: 13 2. Some or all leaves scale-like and the scale-like leaves less than 1/8 inch long, overlapping in pairs, and closely appressed to twigs (fig. 5b): 3 2. Leaves all needlelike (fig. 5a), 3/16 inch or more long, pointing away from twigs: 4 3. Leafy twigs flattened with only scale-like leaves; cones woody: arborvitae or northern white cedar, Thuja occidentalis 3. Leafy twigs angled or round in cross section, usually with both scale-like and needlelike leaves conspicuous; cones fleshy and berrylike: junipers, Juniperus spp.

4. Leaves in fascicles of 2, 3, or 5 (fig. 6): pines, Pinus spp. (key to species on p. 33) 4. Leaves not in fascicles of 2, 3, or 5: 5



fig. 7

5. At least some leaves in dense tufts of 20 to 30 at the ends of short spur shoots (fig. 7): European larch, Larix decidua 5. Spur shoots absent; leaves all alternate or whorled: 6 6. Leaves in whorls of 3, conspicuously whitened on their upper surfaces; seeds in bluish, berrylike cones; plant shrubby, rarely becoming a small tree: common juniper, Juniperus communis 6. Leaves alternate, either green or blue-green above; seeds in woody or papery cones or solitary in red, fleshy cups: 7

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fig. 8

7. Leaves 4-sided and easily rolled between thumb and forefinger with woody, peglike bases that remain on the twigs when the green portions fall (seen on dead twigs) (fig. 8): spruces, Picea spp. (key to species on p. 33) 7. Leaves flat, not easily rolled between thumb and forefinger: 8 8. Buds ovoid, sharp-pointed; cones with protruding 3-pointed bracts between scales: Douglas-fir, Pseudotsuga menziesii 8. Buds subglobose to short-ovoid with rounded or blunt-pointed tips; bracts of cones small and inconspicuous, not protruding between the scales: 9 9. Leaves abruptly tapered to sharppointed tips; seeds, when present, in red, fleshy cups; plant shrubby, rarely becoming a small tree: yews, Taxus spp. 9. Leaves with blunt or rounded tips; seed in cones; a tree: 10

10. Many if not all leaves 1 1/2 to 2 inches long, blue-green on both surfaces: white or concolor fir, Abies concolor 10. Leaves all 3/16 to 1 1/4 inches long, dark green above and either green or whitened below: 11 11. Leaves green on both surfaces; deciduous in autumn: bald­ cypress, Taxodium distichum 11. Leaves dark green above and whitened below, evergreen: 12

fig. 9

12. Leaves with short but distinct petioles (fig. 9); cones 1/2 to 3/4 inch long: eastern hemlock, Tsuga canadensis 12. Leaves without petioles; cones at least 2 inches long, disintegrating when mature: balsam fir, Abies balsamea 13. Leaves compound: 14 13. Leaves simple: 38 14. Leaves opposite: 15 14. Leaves alternate: 16 15. Many if not all leaves with 3 leaflets: 34 15. Leaves all with 5 to 13 leaflets: 17 16. Leaflets 5 or more: 23 16. Leaflets 3: 35 17. Leaflets palmately arranged: 18 17. Leaflets pinnately arranged: 19

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18 i d e n t i f y i n g i o w a ’ s t r e e s

a

b

fig. 10

18. Leaflets abruptly tapered at apex (fig. 10a), usually 7 in number; buds dark brown, sticky: common horsechestnut, Aesculus hippocastanum 18. Leaflets gradually tapered to apex (fig. 10b), usually 5 in number but sometimes 6 or 7; buds light brown, dry: Ohio buckeye, Aescu­ lus glabra 19. Twigs green or purple, usually with a white, waxy coating; buds white-hairy; leaflets 3, 5, or 7: boxelder, Acer negundo 19. Twigs gray; buds glabrous; leaflets mostly 7, 9, or 11: 20

a fig. 11

b

20. Leaflets closely and conspicuously toothed (fig. 11a): 22 20. Leaflets either entire or with a few inconspicuous and widely spaced teeth (fig. 11b): 21

21. Buds hidden within bases of petioles; fruit a drupe; rare cultivated tree: Amur corktree, Phelloden­ dron amurense 21. Buds visible in leaf axils and at twig tips; fruit a paddle-shaped samara: white ash, Fraxinus americana 22. Terminal bud lacking on most if not all twigs; fruit a purple berry; tall shrub with weak, pithy stems: common elderberry, Sambucus canadensis 22. Terminal bud present; fruit a paddle-shaped samara; a tree: ashes, Fraxinus spp. (key to species on p. 32) 23. Leaflets closely and conspicuously toothed (fig. 11a): 24 23. Leaflets either entire or with a few inconspicuous and widely spaced teeth (fig. 11b): 29 24. Leaflets 1 to 2 1/4 inches long and 1/2 to 3/4 inch wide; fruit a small, berrylike orange or orange-red pome: European mountain-ash, Sorbus aucuparia 24. Largest leaflets more than 2 1/4 inches long and 3/4 inch wide; fruit a nut or drupe: 25 25. Terminal bud absent, lateral buds hidden by bases of petioles; fruit a small red drupe: sumacs, Rhus spp. (key to species on p. 38) 25. Terminal bud present, lateral buds normally visible in leaf axils; fruit a nut: 26

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26. Leaflets 5, 7, or 9: hickories, Carya spp. (key to species on p. 30) 26. Leaflets 11 to 23: 27 27. Leaflets conspicuously curved in shape; pith of twigs continuous; husk of nut with 4 ridges: pecan, Carya illinoensis 27. Leaflets not curved; pith chambered; husk lacking ridges: 28 28. Terminal bud subglobose, gray, 3/16 to 1/3 inch long; nut round; trunk bark dark gray or black: black walnut, Juglans nigra 28. Terminal bud ovoid-elongate, yellow-brown, 3/8 to 3/4 inch long; nut football-shaped; trunk bark light gray: butternut, Juglans cinerea 29. Twigs bearing thorns or spines: 30 29. Twigs not thorny or spiny: 32 30. Twigs bearing branched thorns at least 3/4 inch long: honey locust, Gleditsia triacanthos 30. Twigs bearing unbranched spines 1/2 inch or less long in pairs at bases of petioles: 31 31. Leaflets stalkless or nearly so, marked with tiny translucent dots (seen against strong light); buds red, visible in leaf axils and at twig tips: prickly-ash, Zantho­ xylum americanum 31. Leaflets with thick stalks 1/8 to 1/4 inch long, not marked with dots; buds hidden by bases of petioles, so apparently absent: black locust, Robinia pseudoacacia

32. Leaflets less than 3/4 inch wide: 33 32. Largest leaflets 3/4 to 3 inches wide: 36 33. Leaflets entire, often marked with tiny dots (seen against strong light); leaves strictly oncepinnate; tall shrub with slender stems: indigo bush, Amorpha fruticosa 33. Leaflets distantly and obscurely toothed, not marked with dots; leaves once- or twice-pinnate with both types often present on the same tree: honey locust, Gleditsia triacanthos var. inermis 34. Leaflets entire or with no more than 5 teeth per inch of margin: boxelder, Acer negundo 34. Leaflets with 10 to 20 teeth per inch of margin: bladdernut, Staphylea trifolia 35. Buds hidden by bases of petioles, so apparently absent; fruit a 2-seeded, elmlike samara: hoptree, Ptelea trifoliata 35. Buds visible in leaf axils or at twig tips; fruit a drupe: sumacs, Rhus spp. (key to species on p. 38) 36. Leaves twice-pinnately compound: Kentucky coffee tree, Gymnocladus dioicus 36. Leaves once-pinnately compound: 37

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20 i d e n t i f y i n g i o w a ’ s t r e e s

a

b

fig. 12

fig. 14

37. Base of each leaflet with 1 or 2 gland-tipped teeth (fig. 12); twigs very stout: tree-of-heaven, Ailan­ thus altissima 37. Bases of leaflets lacking glandtipped teeth; twigs slender: yellowwood, Cladrastis kentukea 38. Leaves lobed: 39 38. Leaves not lobed: 51 39. Leaves opposite: maples, Acer spp. (key to species on p. 28) 39. Leaves alternate: 40

41. Leaves palmately veined (i.e., having 3 or 5 equally prominent veins originating from point where petiole joins blade, with numerous smaller veins branching from these) (fig. 14a): 42 41. Leaves pinnately veined (i.e., having a single prominent midvein and numerous smaller veins branching from it at more or less regular intervals) (fig. 14b): 46 42. Buds hidden within swollen bases of petioles; stipules or their scars forming ring around twig at base of each petiole: sycamore, Platanus occidentalis 42. Bud visible in leaf axils; stipules not encircling twigs: 43 43. Leaves white beneath; bark on upper trunk and larger branches white with black markings: white poplar, Populus alba 43. Leaves green beneath; bark gray, brown, or light orange: 44 44. Leaves star-shaped; fruit a woody, prickly ball: sweetgum, Liquidambar styraciflua 44. Leaves not star-shaped; fruit blackberrylike: 45

fig. 13

40. Leaves half-round or fan-shaped with 2 or more lobes and numerous crowded, nearly parallel veins (fig. 13): ginkgo, Ginkgo biloba 40. Leaves neither half-round nor fan-shaped, veins freely branching: 41

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a fig. 15

48. Lobed and unlobed leaves present on same tree and often on same twig: sassafras, Sassafras albidum 48. Leaves all lobed: 49

b

45. Leaves glabrous or with hairs restricted to largest veins beneath, their lobes gradually tapered to blunt or short-pointed tips (fig. 15a), leaves usually 2 to 4 inches long: white mulberry, Morus alba 45. Leaves hairy along large and small veins beneath, their lobes abruptly tapered to long-pointed tips (fig. 15b), largest leaves 4 to 9 inches long: red mulberry, Morus rubra

a fig. 16

b

c

46. Leaf lobes entire or with a few bristle-tipped teeth at tips (fig. 16a, b); twigs never thorny: 47 46. Leaf lobes closely toothed (fig. 16c); twigs often thorny: 50 47. Leaves with 5 to 11 lobes: oaks, Quercus spp. (key to species on p. 36) 47. Leaves with 2, 3, or 4 lobes: 48

fig. 17

49. Leaves 4-lobed with notched apex (fig. 17): tulip tree, Lirioden­ dron tulipifera 49. Leaves 3-lobed with rounded apex: blackjack oak, Quercus marilandica 50. Buds pubescent; thorns, when present, with leaves or leaf scars along their surfaces: crabapples, Malus spp. 50. Buds glabrous; surfaces of thorns smooth without leaves or leaf scars: hawthorns, Crataegus spp. (key to species on p. 32) 51. Leaves entire: 52 51. Leaves toothed: 67 52. Leaves opposite or in whorls of 3: 53 52. Leaves alternate: 57 53. Leaves in whorls of 3 at some or all nodes: 54 53. Leaves opposite at all nodes: 55

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22 i d e n t i f y i n g i o w a ’ s t r e e s 54. Leaves broadest near base, 6 to 12 inches long; fruit a pencil-shaped pod 6 or more inches long; a tree: northern catalpa, Catalpa speciosa 54. Leaves broadest near middle, 3 to 6 inches long; fruit ballshaped, less than 1 inch in diameter; a large shrub: buttonbush, Cephalanthus occidentalis

a fig. 18

b

c

55. Leaf veins strongly curved, following margins (fig. 18a); each bud enclosed by a single pair of scales: dogwoods, Cornus spp. (key to species on p. 31) 55. Leaf veins straight or only slightly curved, branching freely near margins (fig. 18b, c); each bud enclosed by several pairs of overlapping scales: 56 56. Leaves broadly ovate with petioles 3/8 or more inch long; flowers and fruits (capsules) in large panicles at tips of twigs: lilacs, Syringa spp. 56. Leaves not broadly ovate with petioles no more than 1/4 inch long; flowers and fruits (berries) in pairs from axils of leaves: honeysuckles, Lonicera spp.

57. Leaves half-round or fan-shaped with numerous crowded, nearly parallel veins (fig. 13): ginkgo, Ginkgo biloba 57. Leaves neither fan-shaped nor half-round, their veins freely branching: 58 58. Leaves nearly round, each with several large veins meeting at base of blade: redbud, Cercis canadensis 58. Leaves distinctly longer than wide, each with a single large vein in middle and several smaller veins branching from it at more or less regular intervals: 59 59. Lower surfaces of leaves a shiny silver color: 60 59. Lower surfaces of leaves green or white: 61 60. Leaves linear or linear-lanceolate (4 to 7 times longer than wide), silvery on both sides; ripe fruits yellow with a silver coating: Russian-olive, Elaeagnus angustifolia 60. Leaves elliptic or ovate-oblong (2 or 3 times longer than wide), green above; ripe fruits red: autumn-olive, Elaeagnus umbellata

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61. Three or 4 buds clustered at tips of twig, each with many tiny scales arranged in vertical rows; midvein of leaf usually extending beyond apex, forming a short bristle: shingle oak, Quercus imbricaria 61. Buds not clustered at twig tips, each with 0 to 5 visible scales; leaves not bristle-tipped: 62 62. Terminal bud 1/3 to 3/4 inch long with dense covering of soft greenish hairs; stipules or their scars forming ring around twig at base of each petiole or leaf scar: magnolias, Magnolia spp. (key to species on p. 33) 62. Terminal bud absent or lacking a covering of soft greenish hairs if present; stipules or their scars not encircling twigs: 63 63. Leaves 6 to 12 inches long: pawpaw, Asimina triloba 63. Leaves less than 6 inches long: 64 64. Each bud enclosed by a single scale: willows, Salix spp. (key to species on p. 38) 64. Each bud enclosed by 2 to 5 scales: 65 65. Leaf veins strongly curved, following margin (fig. 18a); fruit 1/4 to 1/3 inch in diameter: alternateleaf dogwood, Cornus alternifolia 65. Leaf veins straight or only slightly curved, forming a network near margin (fig. 18b, c); fruit 3/4 inch or more in diameter: 66



fig. 19

66. Two dark-colored scales from last year’s bud persisting at base of each shoot (twig) of current growing season (fig. 19); fruit 3/4 to 1 1/2 inches in diameter; twigs not thorny: persimmon, Diospyros virginiana 66. Scales from last year’s bud not persisting at twig base; fruit a green, warty ball 3 to 5 inches in diameter; twigs often thorny: Osage orange, Maclura pomifera 67. Leaves opposite or subopposite (i.e., associated in pairs at nodes but not exactly opposite): 68 67. Leaves alternate: 72 68. Leaf veins strongly curved, following margins (fig. 18a); twigs usually tipped by short thorns: common buckthorn, Rhamnus cathartica 68. Leaf veins straight or slightly curved, not following margins (fig. 18b, c); twigs tipped by buds: 69

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24 i d e n t i f y i n g i o w a ’ s t r e e s

a fig. 20

b

69. Largest veins ending near the margin, forming network of many smaller veins (fig. 20a): 71 69. Largest veins running straight to tips of teeth, branched or not (fig. 20b): 70 70. Leaves appearing opposite on previous year’s growth only, alternate on shoots of the current season: birches, Betula spp. (key to species on p. 30) 70. Leaves strictly opposite: maples, Acer spp. (key to species on p. 28)

fig. 21

71. Terminal bud 3/8 to 1 inch long, enclosed by single pair of scales; petioles slightly winged (fig. 21); fruit a drupe: nannyberry, Vibur­ num lentago 71. Terminal bud less than 3/8 inch long, enclosed by 3 or 4 pairs of scales; petioles not winged; fruit a small capsule with drupelike seeds: wahoo, Euonymus atropurpureus

72. Upper portion of petioles vertically flattened: poplars, Populus spp. (key to species on p. 34) 72. Upper portion of petioles round: 73 73. Each leaf with 3 or more large veins originating from point where blade joins petiole, with smaller veins branching from these at more or less regular intervals (fig. 14a): 74 73. Each leaf with single large vein in middle and several smaller veins branching from it at regular intervals (fig. 14b): 78 74. Leaves about twice as long as wide, broadest at base; pith of twigs intermittently chambered: hackberry, Celtis occidentalis 74. Leaves round or only slightly longer than wide, usually broadest near middle; pith continuous: 75 75. Largest leaves 4 to 9 inches long: 76 75. Largest leaves 2 to 4 inches long: 77 76. Leaves hairy along smaller veins beneath; bud scales 3 to 7: red mulberry, Morus rubra 76. Leaves glabrous except for tufts of hair in angles of largest veins beneath; bud scales usually 2: American basswood, Tilia americana

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77. Leaves longer than wide, gradually tapered to blunt or shortpointed tips (fig. 15a); bud scales 3 to 7: white mulberry, Morus alba 77. Leaves nearly round, abruptly tapered to long-pointed tips (fig. 15b); bud scales usually 2: littleleaf  linden, Tilia cordata 78. Leaves 5 to 12 times longer than wide: willows, Salix spp. (key to species on p. 38) 78. Leaves 1 to 4 times longer than wide: 79

fig. 22

79. Small, lumplike glands present on upper portion of petiole near its junction with blade (fig. 22): 80 79. Petioles lacking glands: 81 80. Each bud enclosed by a single scale; flowers lacking petals, in catkins; fruit a small, flaskshaped capsule present only in spring and early summer: willows, Salix spp. (key to species on p. 38) 80. Each bud enclosed by several scales; flowers with showy white petals, in racemes or umbellike clusters; fruit a drupe ripening in summer or fall: cherries and plums, Prunus spp. (key to species on p. 35)

a

b

fig. 23

81. Leaves conspicuously uneven at base (fig. 23a): 82 81. Leaves equal or nearly so at base (fig. 23b): 85 82. Leaves wavy-margined with tiny, widely spaced teeth; buds naked: witch-hazel, Hamamelis virginiana 82. Leaves with conspicuous, closely spaced teeth; buds enclosed by scales: 83 83. Leaves alternate on twigs but paired at tips of short spur shoots on branchlets; twigs with faint taste of wintergreen: yellow birch, Betula alleghaniensis 83. Leaves strictly alternate; twigs lacking wintergreen taste: 84

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26 i d e n t i f y i n g i o w a ’ s t r e e s

a fig. 24

b

84. Each half of leaf blade with 4 to 7 large veins ending near margin, forming network of numerous tiny veins (fig. 24a); buds enclosed by 3 or 4 scales: hackberry, Celtis occidentalis 84. Each half of leaf blade with 7 or more large veins that run straight to tips of teeth (fig. 24b); buds enclosed by 6 or more scales: elms, Ulmus spp. (key to species on p. 39) 85. Largest leaf veins either ending near margin or curving upward and following margin, then branching into several tiny veins that run into teeth (fig. 20a): 98 85. Largest leaf veins running straight to tips of teeth, branched or not (fig. 20b): 86 86. Leaves with 2 to 5 teeth per inch of margin at midleaf: 87 86. Leaves with more than 5 teeth per inch of margin at midleaf: 89

87. Leaf teeth tiny and rather inconspicuous; buds elongate, 3/8 to 1 inch long; trunk bark very smooth: American beech, Fagus grandifolia 87. Leaf teeth large and prominent; buds ovoid, about 1/4 inch long; trunk bark scaly or furrowed: 88 88. Buds clustered at twig tips, each with numerous tiny scales arranged in vertical rows; bases of nuts enclosed in cuplike structures: oaks, Quercus spp. (key to species on p. 36) 88. Buds solitary at twig tips, each with 2 or 3 visible scales; nuts enclosed in large, spiny burs: American chestnut, Castanea dentata 89. Twigs thorny: 90 89. Twigs not thorny: 91 90. Thorns bearing leaves or leaf scars: prairie crabapple, Malus ioensis 90. Thorns smooth without leaves or leaf scars: hawthorns, Crataegus spp. (key to species on p. 32) 91. Leaves alternate on twigs but paired at ends of spur shoots on branchlets: birches, Betula spp. (key to species on p. 30) 91. Leaves strictly alternate; spur shoots absent: 92

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92. Lateral buds stalked, each with 2 scales that meet along edges without overlapping; fruit conelike, 3/8 to 3/4 inch long: 93 92. Lateral buds not stalked, each with several overlapping scales; fruit not conelike: 94 93. Each half of leaf blade with 5 or 6 large veins; cultivated tree: European black alder, Alnus glutinosa 93. Each half of leaf blade with 8 or more large veins; native shrub, northeastern Iowa: speckled alder, Alnus rugosa 94. Leaves with blunt or rounded tips; fruit a small, berrylike pome: serviceberries, Amelanch­ ier spp. (key to species on p. 29) 94. Leaves with pointed tips; fruit a small nut or samara: 95 95. Petioles and twigs covered with stiff, erect, gland-tipped hairs; tall native shrub, often forming thickets in upland woods and wood edges: American hazel, Corylus americana 95. Petioles and twigs glabrous or with tiny appressed hairs; a tree: 96

96. Bud scales marked with fine parallel lines (seen with magnifying glass); leaves very soft to touch; fruits (nuts) in small papery sacs that hang from twigs in hoplike clusters: ironwood or hop hornbeam, Ostrya virginiana 96. Bud scales not marked with parallel lines; leaves either smooth or very rough to the touch; fruits not in papery sacs: 97 97. Bud scales arranged in 2 rows; fruit a samara; trunk bark scaly or furrowed: elms, Ulmus spp. (key to species on p. 39) 97. Bud scales arranged in 4 rows; fruit a small nut subtended by 3-pointed, leaflike bract; trunk bark very smooth: American hornbeam, Carpinus caroliniana 98. Each bud enclosed by a single scale: willows, Salix spp. (key to species on p. 38) 98. Each bud enclosed by several scales: 99 99. Terminal bud fragrant when crushed, sticky, over 5/8 inch long; flowers without petals, in catkins; fruit a small, flaskshaped capsule present only in late spring and early summer: balsam poplar, Populus balsamifera 99. Terminal bud lacking the above combination of characteristics or absent; flowers with showy white or pink petals; fruit a drupe or pome: 100

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28 i d e n t i f y i n g i o w a ’ s t r e e s 100. Terminal bud elongate; flower petals mostly 3 to 4 times longer than wide; fruit a small, berrylike pome ripening in early summer: serviceberries, Amelanchier spp. (key to species on p. 29) 100. Terminal bud, if present, either ovoid or subglobose; petals round or only slightly longer than wide; fruit ripening in midto late summer or autumn: 101 101. Each flower with 2 to 5 styles; fruit (pome) with more than 1 seed: apples, crabapples, and pears, Malus and Pyrus spp. 101. Each flower with 1 style; fruit (drupe) 1-seeded: cherries and plums, Prunus spp. (key to species on p. 35)

Key to Maples (Acer) 1. Leaves compound: boxelder, A. negundo 1. Leaves simple: 2 2. Leaf margins entire or with 1 or 2 pairs of teeth per lobe; trunk bark of larger trees dark and furrowed (hard maples): 3 2. Leaf margins conspicuously toothed with 3 to 15 pairs of teeth per lobe; trunk bark light gray, either smooth or scaly (soft maples): 5

3. Terminal bud plump, blunt, green changing to reddish purple with 2 or 3 pairs of visible scales; petioles usually exuding a drop of milky sap when broken, especially in spring and early summer: Norway maple, A. platanoides 3. Terminal bud slender, pointed, brown, with 5 to 9 pairs of visible scales; petioles with clear, watery sap (native hard maple). This tree can be divided into 2 more or less distinct forms, which botanists have variously interpreted as 2 species or varieties of a single species. Typical representatives of each form key out as follows: 4. Leaves entire or nearly so, finely hairy beneath, with 3 drooping lobes; sinuses between lobes forming right angles; petiole bases of most leaves with small leaflike stipules: black maple, A. nigrum 4. Leaves toothed, glabrous beneath, with 5 nondrooping lobes; sinuses forming acute angles; petiole bases without stipules: sugar maple, A. saccharum 5. Leaves about as wide as long (measure width as distance between tips of 2 largest lateral lobes): 6 5. Leaves 1 1/2 to 2 times longer than wide: Amur maple, A. ginnala

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6. Leaves deeply lobed with largest pair of sinuses extending about 3/4 of the distance from apex to base of leaf; central lobe widest near middle, tapering to both apex and base: silver maple, A. saccharinum 6. Leaves shallowly lobed with largest sinuses extending only 1/3 to 1/2 of the distance to base of leaf; central lobe widest at base, gradually tapering to apex: 7 7. Terminal bud with 2 or 3 pairs of visible scales; introduced ornamental tree: red maple, A. rubrum 7. Terminal bud with single pair of visible scales; small native tree of steep wooded slopes; extreme northeastern Iowa: mountain maple, A. spicatum

Key to Serviceberries (Juneberries) (Amelanchier)

S erviceberries are difficult to distinguish from one another, and the genus needs further study in Iowa. The following key will identify typical individuals of our native species. A. ×grandiflora, a hybrid between the downy and Allegheny serviceberries, is often seen in cultivation. Its young leaves are pubescent and purpletinged; mature leaves are glabrous.

1. Suckering, colonial shrub: 2 1. Tree or shrub with one to several clumped stems: 3 2. Leaves nearly round, broadly rounded to truncate at apex; rare shrub of prairie regions in northwest and north central Iowa: saskatoon, A. alnifolia 2. Leaves elliptic to oblong; shrub native in north central and northeastern Iowa: low serviceberry, A. humilis (A. spicata) 3. Leaves coarsely toothed with their veins either not forked or once forked and running straight into the tips of the teeth: round-leaf serviceberry, A. sanguinea 3. Leaves finely toothed with their veins branching freely near the margin and forming a network of many tiny veins: 4 4. Top of ovary densely pubescent with some of this pubescence persisting in fruit; native in northeastern Iowa only: inland serviceberry, A. interior 4. Top of ovary glabrous: 5 5. Leaves densely white-hairy beneath when young, becoming nearly glabrous when full-grown; native tree of eastern, southern, and central Iowa: downy serviceberry, A. arborea 5. Leaves glabrous at all stages of development; tree native in northeastern Iowa: Allegheny serviceberry, A. laevis

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Key to Birches (Betula) 1. Leaves rounded or roundish at apex; rare shrub of wetlands in northern Iowa: dwarf  birch, B. pumila 1. Leaves pointed; trees: 2 2. Trunk bark gray, brown, gold, orange, or mixed orange and white: 5 2. Trunk bark uniformly white or white with black markings. These species are variable and not easily distinguished from one another, but typical specimens differ as follows: 3. Leaves as broad as or broader at middle than at base, tapered only on upper third of margin; native tree, sometimes cultivated: paper birch, B. papyrifera 3. Leaves broadest below middle, gradually tapered to pointed tips; introduced ornamental tree: 4

a fig. 25

b

c

4. Leaf bases wedge-shaped (fig. 25a); leaves glabrous beneath: European white birch, B. pendula 4. Leaf bases truncate (fig. 25c) to slightly heart-shaped; leaves usually with tufts of hairs in the vein axils beneath: Asian white birch, B. platyphylla

5. Leaves with wedge-shaped bases (fig. 25a) and 7 to 9 veins on each side; bark separating into papery flakes or scales, at first orange or mixed orange and white, later orange-brown to gray: river birch, B. nigra 5. Leaves with rounded bases (fig. 25b) and 9 to 12 veins on each side; bark smooth at first but becoming scaly, gray to gold in color: yellow birch, B. alleghaniensis

Key to Hickories (Carya) 1. Many if not all leaves with 5 leaflets: shagbark hickory, C. ovata 1. Leaves with 7 or more leaflets: 2 2. Leaflets conspicuously curved, usually 11 to 17 in number: pecan, C. illinoensis 2. Leaflets not noticeably curved, usually 7 to 9 in number: 3 3. Terminal bud slender, covered with 2 bright yellow scales that meet along edges without over­ lapping; husk of nut less than 1/8 inch thick: bitternut hickory, C. cordiformis 3. Terminal bud plump, covered with several brown or tan overlapping scales; husk 1/8 to 1/2 inch thick: 4

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s u m m e r k e y s t o i o w a ’ s t r e e s 31

4. Leaves 15 to 22 inches long, petioles glabrous or nearly so; bark of larger trees separating into large, flat, loosely attached pieces that give the trunk a shaggy appearance; tree of floodplain woods: shellbark hickory, C. laciniosa 4. Leaves with hairy petioles, usually less than 15 inches long; trunk bark shallowly furrowed; tree of dry upland woods: mockernut hickory, C. tomentosa

Key to Dogwoods (Cornus)

1. Small cultivated tree with red fruits and large bulb-shaped flower buds: 2 1. Native tree or shrub with white or blue fruits and small ovoid buds: 4 2. Flowers bright yellow: corneliancherry dogwood, C. mas 2. Flowers with large white “petals” and greenish centers: 3 3. Trees blooming in May; fruits in small bunches: flowering dogwood, C. florida 3. Trees blooming in June; fruits in a roundish composite cluster resembling a raspberry: kousa dogwood, C. kousa 4. Leaves alternate: alternate-leaf dogwood, C. alternifolia 4. Leaves opposite: 5

5. Stems and twigs bright red or yellow: red-osier dogwood, C. stolonifera 5. Stems gray, brown, reddish brown, or greenish; twigs red or not: 6 6. Leaves round or nearly so with 6 to 8 pairs of veins; stems green blotched with purple: roundleaf dogwood, C. rugosa 6. Leaves much longer than wide with 3 to 5 pairs of veins; stems some other color: 7 7. Lower surfaces of leaves covered with short, curved hairs that are quite conspicuous through a magnifying glass; upper surfaces of leaves usually rough: roughleaf dogwood, C. drummondii 7. Lower surfaces of leaves glabrous or with scattered short, straight hairs; upper leaf surfaces usually smooth: 8 8. Twigs of current growing season glabrous or nearly so; inflorescence open and panicle-like, about as tall as wide, with bright red stems; fruits white when ripe in late summer: gray dogwood, C. foemina ssp. racemosa 8. Twigs hairy; inflorescence compact and flat-topped with greenish stems; fruits blue when ripe: silky dogwood, C. amomum ssp. obliqua

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32 i d e n t i f y i n g i o w a ’ s t r e e s

Key to Hawthorns (Crataegus)

The genus Crataegus is very difficult taxonomically and needs more study in Iowa. Only the most common species are keyed below. 1. Leaves prominently lobed, widest near base: 2 1. Leaves unlobed or shallowly lobed, widest near the middle or above, with wedge-shaped bases: 3 2. Leaves 2 1/2 to 4 inches long, usually somewhat hairy beneath, their veins running to the lobe tips but not to the sinuses; native tree, sometimes cultivated: downy hawthorn or red haw, C. mollis 2. Leaves 1 to 2 1/2 inches long, glabrous or nearly so, their veins running to the lobe tips and sinuses; cultivated tree: Washington hawthorn, C. phaenopyrum 3. Leaves glossy above; fruits usually 1- or 2-seeded: cockspur hawthorn, C. crus-galli 3. Leaves not glossy; fruits 3- to 5-seeded: 4 4. Leaves glabrous; fruits 3/8 to 1/2 inch in diameter, usually 3-seeded: Margaret’s hawthorn, C. margaretta 4. Leaves hairy at least along the veins beneath; fruits 1/2 to 3/4 inch in diameter, usually 5-seeded: dotted hawthorn, C. punctata

Key to Ashes (Fraxinus) 1. Twigs square in cross section with 4 corky wings along angles; flowers perfect; rare native tree of dry bluffs, extreme eastern Iowa: blue ash, F. quadrangulata 1. Twigs round, not winged; flowers imperfect; widely distributed tree: 2 2. Leaflets on stalks 3/16 to 1/2 inch long, margins either entire or distantly and rather obscurely toothed; wing of samara not extending along edge of seed cavity: white ash, F. americana 2. Leaflets unstalked or on short stalks up to 3/16 inch long, margins conspicuously toothed; wing of samara extending along edge of seed cavity: 3 3. Leaflets short-stalked, usually 7 per leaf, glabrous or with white hairs; wing of samara extending along upper half of seed cavity, which is round in cross section: green ash, F. pennsylvanica 3. Leaflets unstalked, 9 or 11 per leaf, usually with tufts of orange-brown hairs at junctions with rachis (leaf stem); wing of samara extending to base of flattened and rather indistinct seed cavity: black ash, F. nigra

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Key to Magnolias (Magnolia)

1. Flowers green, appearing after leaves in late spring; large tree with brown, scaly, or furrowed bark: cucumber tree, M. acuminata 1. Flowers white or pink, appearing before leaves in early spring; small tree with smooth gray bark: 2 2. Flowers with 9 petallike parts (3 sepals and 6 petals), pink or pinkish in color; terminal buds 1/2 to 3/4 inch long: saucer mag­ nolia, M. ×soulangeana 2. Flowers with 12 to 18 petallike parts (3 sepals and 9 to 15 petals), usually white; terminal buds 1/3 to 1/2 inch long: star magnolia, M. stellata

Key to Spruces (Picea) 1. Cones 4 to 6 inches long; twigs and smaller branches usually drooping: Norway spruce, P. abies 1. Cones less than 4 inches long; twigs and smaller branches more or less horizontal: 2

2. Cones more than 2 1/2 inches long, their scales with irregularly toothed margins; young twigs orange; leaves 3/4 to 1 1/4 inches long, often (but not always) strongly blue-green in color, very sharp-pointed: blue spruce, P. pungens 2. Cones less than 2 1/2 inches long, their scales with entire (unbroken) margins; young twigs gray; leaves dark green to light blue-green, often less than 3/4 inch long: white spruce, P. glauca

Key to Pines (Pinus) 1. Leaves in fascicles of 5: eastern white pine, P. strobus 1. Leaves in fascicles of 2 or 3: 2 2. Leaves 3/4 to 3 inches long: 3 2. Leaves more than 3 inches long: 6 3. Cone scales tipped by sharp prickles 1/16 to 1/8 inch long; tree common on coal spoils in southern Iowa, rarely seen elsewhere: Virginia pine, P. virginiana 3. Cone scales lacking prickles or with inconspicuous prickles less than 1/16 inch long; widely planted: 4

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34 i d e n t i f y i n g i o w a ’ s t r e e s 4. Small ornamental tree branching freely near the ground, producing several arching trunks of equal size instead of one central trunk: mugo pine, P. mugo 4. Tree with single erect trunk and numerous more or less horizontal branches: 5

a b fig. 26

8. Leaves less than 1/16 inch thick, breaking readily when bent double; buds brown; cones mostly under 2 inches long, the fallen ones with a pronounced basal cavity because the lower scales are missing: red pine, P. resinosa 8. Leaves 1/16 to 1/8 inch thick, not breaking readily when bent double; buds more or less covered with a white waxy material; cones 2 to 3 inches long, the fallen ones lacking a basal cavity: Austrian pine, P. nigra

c

5. Leaves 1 to 3 inches long, the 2 leaves in each fascicle parallel or only slightly spread apart (fig. 26a, b); bark orange on upper trunk and larger branches: Scots pine, P. sylvestris 5. Leaves 3/4 to 1 1/2 inches long, the 2 leaves in each fascicle spread widely apart (fig. 26c); bark gray: jack pine, P. banksiana 6. Leaves all 3 to 4 inches long: Scots pine, P. sylvestris 6. Many if not all leaves over 4 inches long: 7 7. Leaves in fascicles of 2 and 3 on same tree: ponderosa pine, P. ponderosa 7. Leaves all in fascicles of 2: 8

Key to Poplars (Populus) 1. Leaves triangular or diamondshaped: 2 1. Leaves round or broadly ovate: 3 2. Leaves with 5 to 9 teeth per inch of margin and tiny glands at junction of petiole and blade; terminal bud 3/8 to 3/4 inch long: eastern cottonwood, P. deltoides 2. Leaves with 12 or more teeth per inch of margin, lacking glands at junctions of petioles and blades; terminal bud 3/16 to 1/4 inch long: Lombardy poplar, P. nigra var. italica 3. Each half of leaf blade with 20 to 40 small, rounded teeth: 4 3. Each half of leaf  blade with 3 to 15 large, blunt teeth or shallow lobes: 5

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4. Leaves round, upper portion of petiole distinctly flattened: quaking aspen, P. tremuloides 4. Leaves ovate with round petioles: balsam poplar, P. balsamifera 5. Leaves green beneath when mature, petiole strongly flattened: bigtooth aspen, P. grandidentata 5. Leaves white beneath, petiole slightly flattened: white poplar, P. alba

Key to Cherries and Plums (Prunus) 1. Leaves reddish purple: 2 1. Leaves green: 3 2. Leaves green at first but changing to reddish purple with small glands on upper portions of petioles; flowers and fruits in racemes at ends of leafy shoots: chokecherry, P. virginiana ‘Shubert’ 2. Leaves reddish purple throughout growing season, usually without glands on petioles; flowers and fruits solitary or paired on twigs of previous growing season: purpleleaf plums (Several small cultivated trees key out here. Most are hybrids or cultivars of P. cerasifera.) 3. Fruits 1/4 to 3/8 inch in diameter (wild cherries): 4 3. Fruits 3/4 inch or more in diameter (plums, peach): 9

4. Leaves oblanceolate with few widely spaced teeth; dwarf shrub of sandy or rocky prairies: 5 4. Leaves of other shapes with closely toothed margins; tall shrub or tree: 6 5. Stems upright; sandy areas in northern and eastern Iowa: sand cherry, P. pumila 5. Stems declining or lying on ground; rock outcrops in extreme northwest Iowa: dwarf cherry, P. besseyi

a fig. 27

b

6. Leaves with sharp, outwardpointing teeth (fig. 27a): 7 6. Leaves with blunt or incurved teeth (fig. 27b): 8 7. Petals of flowers about twice as long as stamens; pit of fruit with corrugated surface; introduced ornamental tree: bird cherry (May tree), P. padus 7. Petals and stamens nearly equal in length; pit of fruit with smooth surface; small native tree, occasionally cultivated: chokecherry, P. virginiana

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36 i d e n t i f y i n g i o w a ’ s t r e e s 8. Flowers and fruits in racemes on leafy shoots (twigs) of current growing season; leaves frequently with orange hairs along lower portion of midvein beneath; tall tree with scaly bark: black cherry, P. serotina 8. Flowers and fruits in small, umbellike clusters on twigs of previous growing season; leaves lacking orange hairs beneath; small tree: pin cherry, P. pensylvanica 9. Leaves lanceolate to oblong, at least twice as long as wide: 10 9. Leave oval to elliptic, less than twice as long as wide: 11 10. Fruits fuzzy: peach, P. persica 10. Fruits smooth: goose plum, P. hortulana 11. Leaf teeth sharp-pointed (fig. 27a): 12 11. Leaf teeth blunt or rounded (fig. 27b): Canada plum, P. nigra 12. Flower stalks glabrous; thicket forming shrub or small tree, common throughout state: American plum, P. americana 12. Flower stalks hairy; tree with single stem, uncommon: big-tree plum, P. mexicana

Key to Oaks (Quercus) 1. Largest veins extending beyond tips of lobes or teeth (or beyond apex of leaf if it is neither toothed nor lobed), forming short bristles (red oaks): 2 1. Lobes or teeth not bristle-tipped (white oaks): 8 2. Leaves unlobed or shallowly 3-lobed: 3 2. Leaves 5- to 9-lobed: 4 3. Leaves elliptic or oblong, not lobed: shingle oak, Q. imbricaria 3. Leaves obovate, shallowly 3-lobed on upper half: blackjack oak, Q. marilandica 4. Length of leaf lobes less than, equal to, or slightly greater than the width of the central, undivided portion of the blade: red oak, Q. rubra 4. Length of largest leaf lobes 2 to 6 times greater than the width of the central, undivided portion of the blade: 5 5. Fully grown buds 1/4 to 1/2 inch long, densely covered with brown hairs; scales around rim of acorncup loosely attached, forming fringe: black oak, Q. velutina 5. Fully grown buds 1/16 to 1/4 inch long, either glabrous or only partially hairy; scales of acorn-cup all tightly attached: 6

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6. Acorn hemisphere-shaped, 3/8 to 1/2 inch long, with a saucer-shaped cup covering only the base of the nut; tree cultivated throughout state but native only in southeastern corner, usually in low-lying woods near streams: pin oak, Q. palustris 6. Acorn longer than wide, 1/2 to 1 inch long, with a bowl-shaped or cone-shaped cup covering about 1/2 of the nut; native or cultivated: Two very similar trees will key out here, variously regarded as different species or varieties of a single species. Both are quite variable and their characteristics overlap. Typical individuals can be identified as follows: 7. Nut egg-shaped with concentric grooves around the apex; cup bowl-shaped; tree cultivated in Iowa but not native: scarlet oak, Q. coccinea 7. Nut elongated, often with dark vertical stripes but lacking concentric grooves around the apex; cup cone-shaped; native tree, occasionally cultivated: Hill’s oak or northern pin oak, Q. ellipsoidalis 8. Leaves glabrous on both surfaces: 9 8. Leaves sparsely to densely hairy beneath (seen with magnifying glass): 10

9. Leaf blades 2 1/2 to 5 inches long with 2 small, earlike projections at base; acorns with stalks longer than leaf petioles; cultivated tree: English oak, Q. robur 9. Leaf blades 5 to 9 inches long without earlike projections at base; acorns not stalked or with stalks shorter than leaf petioles; native tree: white oak, Q. alba 10. Leaves toothed or shallowly lobed (i.e., spaces between lobes or teeth extending less than half the distance between margin and midvein): 11 10. Leaves deeply lobed (i.e., at least some of the spaces between lobes extending more than half the distance between margin and midvein): 13 11. Petioles 1/8 to 3/8 inch long; small, shrubby tree bearing acorns when only a few feet tall: dwarf oak, Q. prinoides 11. Petioles 1/2 to 1 1/2 inches long; a tree: 12 12. Each half of leaf with 8 to 13 often sharp-pointed teeth; acorns unstalked or with very short stalks; tree native in dry upland woods, rarely cultivated: chinkapin oak, Q. muhlenbergii 12. Each half of leaf with 4 to 6 blunt teeth or lobes; acorns with stalks 1 to 4 inches long; tree native in moist, low-lying woods, frequently cultivated: swamp white oak, Q. bicolor

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38 i d e n t i f y i n g i o w a ’ s t r e e s 13. Leaves crosslike in outline with 3 squarish lobes on upper half and 2 to 4 much smaller lobes on lower half; acorn-cup lacking fringe of bristles; rare native tree, extreme southern Iowa: post oak, Q. stellata 13. Leaves irregularly shaped, usually deeply lobed near the middle and shallowly lobed on the upper half, with none or few leaves cross­like in outline; acorn-cup with conspicuous fringe of soft bristles around rim; tree common throughout Iowa: bur oak, Q. macrocarpa

Key to Sumacs (Rhus) 1. Leaves with 3 leaflets: 2 1. Leaves with 11 or more leaflets: 3 2. Terminal leaflet of each leaf on stalk much longer than stalks of other 2 leaflets; terminal bud present; fruit yellowish to white: poison ivy, R. radicans 2. Terminal leaflet of each leaf unstalked or nearly so; terminal bud absent; twigs often tipped by catkinlike cluster of flower buds; fruit red: fragrant sumac, R. aromatica 3. Twigs glabrous: smooth sumac, R. glabra 3. Twigs hairy: staghorn sumac, R. typhina

Key to Willows (Salix) illows vary in size from dwarf W shrubs to tall trees. The following key identifies those that consistently reach tree size. It is impossible to devise a workable key that considers all variations in the foliage of willows, so only typical representatives are considered here. Flowers are often necessary to confirm identification of species. 1. Cultivated tree with spirally twisted or long, drooping branches: 2 1. Branching otherwise; tree cultivated or wild: 3 2. Branches long and drooping, often reaching or nearly reaching the ground: weeping willows, S. ×blanda and S. ×sepulcralis 2. Branches upright, the twigs spirally twisted like corkscrews: corkscrew willow, S. matsudana ‘Tortuosa’ 3. Lower surfaces of leaves light green: 4 3. Lower surfaces of leaves coated with a thin, waxy material making them pale bluish green or white: 5

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4. Leaves distantly toothed (teeth mostly 3 to 10 per inch at midleaf); small tree often forming large thickets: sandbar willow, S. interior 4. Leaves closely toothed (teeth mostly 11 to 25 per inch); mediumsize to large tree: black willow, S. nigra 5. Twigs persistently hairy: 6 5. Twigs glabrous: 7 6. Stipules of vegetative shoots conspicuous, persisting in summer; buds 1/2 to 3/4 inch long, densely hairy: Missouri River willow, S. eriocephala 6. Stipules early deciduous; buds less than 1/2 inch long: white willow, S. alba and its hybrids 7. Bud scales with freely overlapping margins on the back (twig) side of bud (seen with magnifying glass); leaves small and pale green with slender, tail-like tips; petioles long and often twisted, 1/4 to 1/7 as long as the blades: peachleaf willow, S. amygdaloides 7. Bud scale fused into caplike structure with no visible edges; leaves large and dark green: crack willow, S. fragilis and its hybrids

Key to Elms (Ulmus) 1. Leaves mostly 1 to 2 1/2 inches long; buds less than 3/16 inch long: Siberian elm, U. pumila 1. Leaves 2 1/2 to 6 inches long; largest buds 3/16 to 1/4 inch long: 2 2. Leaves very rough above: 3 2. Leaves smooth above: 4 3. Bud scales dark purple, those toward tip of bud more or less covered with shiny, copper-colored hairs; edges of samaras glabrous: slippery elm, U. rubra 3. Bud scales reddish brown with dark margins, usually glabrous; edges of samaras hairy: American elm, U. americana 4. Samaras in racemes; branchlets covered with thick, corky outgrowths: rock elm, U. thomasii 4. Samaras in umbellike clusters; branchlets lacking corky outgrowths: American elm, U. americana

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Winter Keys to Iowa’s Trees Identify ing tr ees in winter is easier than you might expect. Their twigs and fruits are as distinctive as their leaves and easily collected and studied indoors. The only equipment you need is a good magnifying glass. The following key identifies most species you are likely to encounter in Iowa. Hawthorns, dogwoods, apples, most crabapples and pears, lilacs, and lindens (basswoods) are not keyed to species because accurate identification requires leaves, fruits, and in some cases flowers. Several large native shrubs that are common in the woodland understory and might be mistaken for tree saplings are included. Genera with more than two species — willows, poplars, oaks, elms, maples, and ashes — are keyed in separate sections at the end. The key is based on characteristics of the twigs and persistent fruits, supplemented with bark and distribution where appropriate. When collecting twigs for later identification, select healthy-looking specimens with intact tips and clearly defined leaf scars. When collecting fruits, also collect a healthy twig if possible. Be sure to note each tree’s size, shape, bark type and color, and habitat for future reference. Before you collect any twigs, be certain you can recognize poison ivy in winter. It is a shrub or vine rather than a tree, but it often climbs high on the trunks of trees and produces long, straight branches that can be easily mistaken for those of the tree. Fortunately, poison ivy is easy to recognize with its unique combination of naked yellow-brown buds and alternate, V-shaped leaf scars with more than 3 bundle scars. If you cannot identify a tree after repeated attempts, you may have found a rare species not covered in this key. Try a more complete key such as William Harlow’s Fruit Key and Twig Key to Trees and Shrubs.

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42 i d e n t i f y i n g i o w a ’ s t r e e s

General Key 1. Key to fruits: 2 1. Key to twigs: 34 2. Fruit a ball composed of numerous tiny achenes or drupelike units: 3 2. Fruit otherwise: 4 3. Fruit light brown, about 1 inch in diameter: sycamore, Platanus occidentalis 3. Fruit green, 3 to 5 inches in diameter: Osage orange, Maclura pomifera

a fig. 28

b

c

4. Individual fruits with thin, papery wings (fig. 28): 5 4. Fruits not winged (stalk of fruit cluster winged in some species): 7 5. Fruit paddle-shaped or keyshaped with seed at base (fig. 28a, b): 6 5. Fruit propeller-shaped with seed in center (fig. 28c): tree-of-heaven, Ailanthus altissima 6. Fruits key-shaped, attached to twig in pairs (fig. 28a): maples, Acer spp. (key to species on p. 55) 6. Fruits paddle-shaped, not in pairs (fig. 28b): ashes, Fraxinus spp. (key to species on p. 56)

7. Fruit with 1 seed: 8 7. Fruit with 2 or more seeds: 23 8. Fruit a nut, usually enclosed by a husk, sac, or similar structure: 9 8. Fruit a small, berrylike drupe, never enclosed by a sac or husk: 16 9. Nut seated in bowl-, cone-, or saucer-shaped structure covered with tiny overlapping scales: oaks, Quercus spp. (key to species on p. 54) 9. Nut otherwise: 10 10. Nut 1/3 inch or less long: 11 10. Nut 1 inch long or longer: 12 11. Nut with a lobed, leafy bract at its base: American hornbeam, Car­ pinus caroliniana 11. Nut enclosed by a thin, papery sac: ironwood or hop hornbeam, Ostrya virginiana 12. Nut with a corrugated shell, enclosed by a husk that does not split open: 13 12. Nut with a smooth shell, enclosed by a husk that splits completely or partially: 14 13. Nut round: black walnut, Juglans nigra 13. Nut football-shaped: butternut, Juglans cinerea 14. Shell of nut (actually a large, nutlike seed) dark brown and glossy with a single large, pale spot: horsechestnuts (buckeyes), Aes­ culus spp. (See couplet 53 for key to species.) 14. Shell of nut uniformly white or light brown: 15

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15. Husk less than 1/8 inch thick, splitting about halfway open: bitternut hickory, Carya cordiformis 15. Husk more than 1/8 inch thick, splitting completely open: shagbark hickory, Carya ovata 16. Fruits red in compact, upright clusters: 17 16. Fruits a color other than red, either attached individually to twigs or in small open clusters: 18 17. Twigs hairy: staghorn sumac, Rhus typhina 17. Twigs glabrous: smooth sumac, Rhus glabra 18. Fruit 3/4 to 1 inch long: 19 18. Fruit less than 1/2 inch long: 20 19. Fruit with a strong, rank odor when fresh in early winter; each leaf scar with 2 bundle scars; large tree: ginkgo, Ginkgo biloba 19. Fruit not foul-smelling; each leaf scar with 3 bundle scars; shrub or small tree: American plum, Pru­ nus americana

fig. 29 20. Fruits 1 to several on a branched stalk attached to a thin, papery wing (fig. 29): lindens (basswoods), Tilia spp. 20. Fruits in clusters, not winged: 21

21. Fruits attached individually to the twigs, either solitary or in groups of 2 or 3: 22 21. Fruits in racemes, corymbs, or other branched clusters: Various trees and shrubs that rarely retain their fruit in winter will key out here; go to the twig key (couplet 34) to identify these. 22. Fruits dark purple or black: hackberry, Celtis occidentalis 22. Fruits yellowish gray: Russianolive, Elaeagnus angustifolia 23. Fruit a pod or cone: 24 23. Fruit a berry or small, berrylike pome: 32 24. Fruit a cone: European larch, Larix decidua 24. Fruit a pod: 25 25. Pod (legume) distinctly flattened: 26 25. Pod (capsule) rounded or triangular in cross section: 29 26. Pod 1 to 1 1/2 inches wide with seeds 1/3 to 1/2 inch long: 27 26. Pod 3/8 to 1/2 inch wide with seeds 3/16 inch long: 28 27. Pod 6 to 18 inches long, leathery and usually twisted, with at least 12 seeds; trees often bearing large thorns: honey locust, Gleditsia triacanthos 27. Pod thick and woody, usually less than 6 inches long, with 3 to 9 seeds; thorns never present: Kentucky coffee tree, Gymnocladus dioicus

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44 i d e n t i f y i n g i o w a ’ s t r e e s

a fig. 30

b

c

28. Pod with rounded or abruptly tapered apex (fig. 30a, b); twigs usually bearing small paired spines: black locust, Robinia pseudoacacia 28. Pod gradually tapered to apex (fig. 30c); twigs never spiny: redbud, Cercis canadensis 29. Pod pencil-shaped, 6 to 20 inches long: northern catalpa, Catalpa speciosa 29. Pod no more than 2 inches long: 30 30. Seeds with red fleshy coverings, suspended from small open pods by slender stalks: wahoo, Euony­ mus atropurpureus 30. Seeds without red fleshy coverings: 31 31. Pod inflated and bladderlike, 1 to 2 inches long, with thin, papery walls and usually 3 compartments, never splitting open: bladdernut, Staphylea trifolia 31. Pod slender, up to 3/4 inch long, with leathery walls and 2 compartments, splitting open along 2 seams: lilacs, Syringa spp.

32. Twigs tipped by short thorns or broken stubs; leaf scars subopposite: common buckthorn, Rham­ nus cathartica 32. Twigs thornless or with thorns at the nodes; leaf scars alternate: 33 33. Fruits with several small seeds that occupy the center of the fruit and are separated from the flesh by thin, cartilaginous partitions; thorns absent or, if present, with leaf scars on them: apples, crab­ apples, and pears, Malus and Pyrus spp. 33. Fruits with 2 to 5 large, bony, light-colored seeds that occupy bulk of fruit; twigs bearing smooth thorns without leaf scars: hawthorns, Crataegus spp. 34. Twigs or branchlets bearing thorns, spines, spur shoots, or exposed catkins: 35 34. None of above-named structures present: 50 35. Twigs armed with thorns or spines: 36 35. Twigs not thorny or spiny: 44 36. Twigs armed with stipular spines (spines in pairs at each node, one to either side of leaf scar): 37 36. Twigs armed with thorns (solitary at nodes or at end of twig): 38

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37. Buds apparently absent, actually buried beneath surface of leaf scars: black locust, Robinia pseudoacacia 37. Buds red, clearly visible on surface of twig above each leaf scar: prickly-ash, Zanthoxylum americanum 38. Twigs very slender, densely coated with minute silver-gray scales that can be scratched off with fingernail; dried leaves from previous growing season often persisting on twigs: Russianolive, Elaeagnus angustifolia 38. Twigs not coated with silver-gray scales; dried leaves not persisting in winter: 39 39. Leaf scars subopposite (i.e., associated in pairs at nodes, one on either side of twig, but not exactly opposite); buds dark brown or black; twigs often thorn-tipped: common buckthorn, Rhamnus cathartica 39. Leaf scars alternate; buds (if present) red, white, or light brown: 40 40. Buds and/or leaf scars present along surface of thorns: 41 40. Buds and leaf scars absent from thorns or present only at bases of thorns: 42

41. Buds densely coated with white hairs: prairie crabapple, Malus ioensis 41. Buds glabrous, either red or reddish (sometimes white along margins of scales): American plum, Prunus americana 42. Thorns 1/8 to 1/2 inch long: Osage orange, Maclura pomifera 42. Thorns more than 1/2 inch long: 43 43. Buds red, clearly visible on twigs above leaf scars; twig thorns unbranched (thorns sometimes branched on trunk of tree only): hawthorns, Crataegus spp. 43. Buds brown or embedded in twigs and not visible; thorns usually branched: honey locust, Gleditsia triacanthos 44. Twigs bearing catkins: 45 44. Twigs without catkins: 48 45. Buds globose to subglobose; cat­ kins pale gray-brown; tall shrub of clearings, wood edges, and open woods; often forming thickets: American hazel, Corylus americana 45. Buds ovoid; catkins brown; a tree: 46 46. Lateral buds with 6 or more visible scales; spur shoots absent: ironwood or hop hornbeam, Ostrya virginiana 46. Lateral buds with 3 or 4 visible scales; spur shoots often present on branchlets: 47

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46 i d e n t i f y i n g i o w a ’ s t r e e s 47. Trunk bark white on saplings and mature trees, remaining fairly smooth or separating into thin, papery strips; buds glabrous: paper birch, Betula papyrifera (Similar Eurasian species are not easily distinguished during winter.) 47. Outer bark often white on saplings, though separating into papery scales that peel up and reveal orange inner bark, soon turning orange-brown and later dark gray; buds sometimes hairy: river birch, Betula nigra 48. Each leaf scar with 1 or 2 bundle scars: 49 48. Each leaf scar with 3 or more bundle scars: 50 49. Bundle scar 1: European larch, Larix decidua 49. Bundle scars 2: ginkgo, Ginkgo biloba 50. Leaf scars opposite or subopposite (i.e., associated in pairs but not exactly opposite) or in whorls of 3: 51 50. Leaf scars alternate: 64 51. Leaf scars round, in whorls of 3 at many if not all of the nodes: northern catalpa, Catalpa speciosa 51. Leaf scars opposite or sub­ opposite: 52

52. Buds plump with several overlapping scales, the largest ones 1/2 to 1 inch long; twigs stout with large, shield-shaped, triangular, or halfround leaf scars: 53 52. Characteristics of the buds and twigs not combined as described above: 54 53. Buds dark brown, sticky: common horsechestnut, Aesculus hippocastanum 53. Buds light brown, not sticky: Ohio buckeye, Aesculus glabra

a fig. 31

b

c

54. Bundle scar(s) forming a fine, curved line in each leaf scar (fig. 31): 55 54. Bundle scars not forming a line: 57 55. Bud at end of twig with 2 or 4 visible scales; bundle scars numerous, tiny, and very close together, forming a curved line (fig. 31a): ashes, Fraxinus spp. (key to species on p. 56) 55. Bud(s) at end of twig each with 6 to 10 visible scales; bundle scar 1 in each leaf scar, elongated into a continuous or broken line (fig. 31b, c): 56

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w i n t e r k e y s t o i o w a ’ s t r e e s 47

56. Twigs green or purple, often marked with 4 longitudinal lines; terminal bud present: wahoo, Euonymus atropurpureus 56. Twigs gray or brown, not lined, usually tipped by 2 lateral buds instead of terminal bud: lilacs, Syringa spp. 57. Terminal bud present: 58 57. Terminal bud absent (twig may be tipped by a pair of lateral buds or a short thorn): 61 58. Terminal bud enclosed by 4 to 18 overlapping scales: maples, Acer spp. (key to species on p. 55) 58. Terminal bud with 2 scales: 59 59. Terminal bud 3/8 to 1 inch long: nannyberry, Viburnum lentago 59. Terminal bud shorter than 3/8 inch: 60

a fig. 32

61. Twigs often tipped by short, thornlike projections; leaf scars subopposite: common buckthorn, Rhamnus cathartica 61. Twigs not thorn-tipped; leaf scars mostly opposite: 62 62. Small to large tree with slender twigs: maples, Acer spp. (key to species on p. 55) 62. Large native shrub with twigs moderate to stout: 63 63. Twigs gray or gray-brown with thick pith; stipule scars usually absent: common elderberry, Sambucus canadensis 63. Twigs green or purple; stipule scars present: bladdernut, Staphylea trifolia

b

60. Leaf scars conspicuously raised above surface of twig on persisting petiole bases (fig. 32a): dogwoods, Cornus spp. 60. Leaf scars flush with surface of twig or only slightly raised (fig. 32b); petioles completely deciduous in autumn: maples, Acer spp. (key to species on p. 55)

fig. 33

64. Several buds clustered together at tip of each twig (fig. 33): 65 64. Twigs tipped by 1 or 2 buds or tips of twigs lacking buds: 67

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48 i d e n t i f y i n g i o w a ’ s t r e e s 65. Buds covered with numerous scales usually arranged in vertical rows (fig. 33); leaf scars half-round with many bundle scars; dried leaves from previous growing season sometimes persisting in large numbers: oaks, Quercus spp. (key to species on p. 54) 65. Without the above combination of characteristics: 66

a

fig. 34

b

66. Leaf scars heart-shaped, shieldshaped, rounded, or lobed (figs. 2, p. 8, and 34): 82 66. Leaf scars half-round or broadly crescent-shaped: 103 67. Leaf scars very narrow: ringshaped, linear, crescent-shaped, or U-shaped (fig. 2, p. 8): 68 67. Leaf scars some other shape: 80 68. Terminal buds plump, 3/8 to 3/4 inch long, partly to completely covered with soft hairs: 69 68. Terminal buds absent or, if present, then not as described above: 71

69. Each bud enclosed by a single visible scale; stipule scars forming a fine line from one side of  leaf scar completely around twig to other side: saucer magnolia, Magnolia ×soulangeana 69. Each bud enclosed by 2 or more visible scales; stipule scars not encircling twigs: 70 70. Leaf scars raised above twig on cushionlike bases colored like bud scales; bundle scars usually 5: European mountain-ash, Sorbus aucuparia 70. Leaf scars slightly raised, without obvious cushionlike bases; bundle scars 3: callery pear, Pyrus calleryana 71. Each bud with a single visible scale: 72 (If the buds appear to be absent, go to couplet 91.) 71. Each bud with 3 or more scales or with a dense covering of soft hairs that completely obscure the scales: 73 72. Leaf scars ring-shaped, completely encircling the buds: sycamore, Platanus occidentalis 72. Leaf scars not ring-shaped, not encircling the buds: willows, Salix spp. (key to species on p. 53)

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73. Leaf scars C-shaped, nearly encircling the buds; twigs stout with thick, often conspicuously colored pith: sumacs, Rhus spp. (See couplet 17 for key to species.) 73. Without the above combination of characteristics: 74 74. Buds globose to subglobose (fig. 2, p. 8): 75 74. Buds ovoid to elongate: 76 75. Lateral buds glabrous, with blunt or rounded tips and about half a dozen scales: hawthorns, Cratae­ gus spp. (The tree may have a few long thorns that are scattered and not immediately apparent.) 75. Lateral buds with about 4 scales, usually at least somewhat hairy, usually with pointed tips: crab­ apples, Malus spp. 76. Terminal bud elongate, its length at least 4 times greater than its basal diameter (measure with ruler): downy serviceberry, Amelanchier arborea 76. Terminal bud absent or, if present, with its length no more than 3 times its basal diameter: 77 77. Lateral buds with 3 or 4 scales: 78 77. Lateral buds with about half a dozen scales: 105

a fig. 35

b

78. Lowermost scale of each lateral bud centered directly over leaf scar (fig. 35a): poplars, Populus spp. (key to species on p. 54) 78. Lowermost scale of each lateral bud offset to one side of leaf scar (fig. 35b): 79 79. Ordinary elongated twigs tipped by false terminal buds (terminal buds present only on spur shoots if spur shoots present): birches, Betula spp. (See couplet 47 for key to species.) 79. Terminal bud usually present on both spur shoots and ordinary elongated twigs: crabapples, Malus spp. 80. Leaf scars heart-shaped, shieldshaped, round, or lobed (figs. 2, p. 8, and 34): 81 80. Leaf scars half-round or broadly crescent-shaped or very tiny and inconspicuous: 89 81. Terminal bud present, usually much larger than the laterals: 82 81. Terminal bud absent (twig may be tipped by a false terminal bud the same size and shape as the laterals): 87

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50 i d e n t i f y i n g i o w a ’ s t r e e s 82. Leaf scars with 3 bundle scars each (some of these may be split in two, so that there appear to be 4 to 6 bundle scars in 3 groups; see fig. 35a): 83 82. Leaf scars with numerous bundle scars: 85 83. Pith of twigs chambered; buds usually superposed (in pairs or threes at each leaf scar, one above the other): 84 83. Pith continuous; buds only one at each leaf scar: poplars, Populus spp. (key to species on p. 54) 84. Leaf scar with a fringe of yellowbrown hairs along upper margin (fig. 34a); terminal bud elongated, yellow-brown, 1/3 to 3/4 inch long: butternut, Juglans cinerea 84. Leaf scar not fringed (fig. 34b); terminal bud subglobose, gray, 3/16 to 1/3 inch long: black walnut, Juglans nigra 85. Stipule scars forming a line from one side of each leaf scar completely around twig to other side; terminal buds duckbill-shaped: tulip tree, Liriodendron tulipifera 85. Stipule scars absent; buds ovoid to elongate: 86

86. Terminal bud yellow, slender, with 2 scales that meet along the edges without overlapping: bitternut hickory, Carya cordiformis 86. Terminal bud brown or tan, plump, with several overlapping scales: shagbark hickory, Carya ovata 87. Twigs very stout ( 1/4 to 1/2 inch in diameter) with thick, often brightly colored pith: 88 87. Twigs slender to moderate in diameter (less than 1/4 inch in diameter): 91 88. Buds buried in small, craterlike depressions in twig, with only tips visible; leaf scars heartshaped with 3 to 5 bundle scars: Kentucky coffee tree, Gymno­ cladus dioicus 88. Buds dome-shaped, plainly visible on surface of twig immediately above leaf scars; leaf scars shield-shaped with 7 or more bundle scars: tree-of-heaven, Ailanthus altissima 89. Twigs partly to completely coated with minute silver-gray scales: Russian-olive, Elaeagnus angustifolia 89. Twigs not coated with scales, though sometimes hairy or marked with scattered dots (lenticels): 90

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90. Terminal buds absent (twigs may tipped by false terminal buds, thornlike points, or broken stubs): 91 90. Terminal buds present on most if not all of the twigs: 102 91. Buds buried in twig and thus apparently absent or with their bases buried so that only their tips are visible: honey locust, Gleditsia triacanthos var. inermis 91. Buds plainly visible on surface of twig: 92 92. Buds subglobose, somewhat lopsided, with 2 (occasionally 3) red or reddish scales: lindens (basswoods), Tilia spp. 92. Buds lacking the above combination of characteristics: 93 (The species in couplets 93 to 101 are among the most difficult to identify in winter. Accurate identification requires careful examination of buds and leaf scars, using a 10-power lens. Be sure to examine several buds or leaf scars at each step in the key.) 93. Bundle scars embedded in a brown corky material covering each of the leaf scars: elms, Ulmus spp. (key to species on p. 55) 93. Leaf scars not covered with a brown corky material: 94

94. Leaf scars round or roundish, conspicuous; bundle scars more than 3 in each leaf scar, either scattered or arranged in a circular pattern: 95 94. Leaf scars half-round or broadly crescent-shaped, very small, with 1 to 3 bundle scars (leaf scars may be so small that bundle scars are indistinct even with magnification): 96 95. Buds about as long as wide, closely flattened against side of twig; bark of branches (and trunks of small trees) pale orange-brown: white mulberry, Morus alba 95. Buds decidedly longer than wide, pointing away from twig at slight angle; bark of branches gray or brown: red mulberry, Morus rubra 96. Largest buds with 1 to 4 scales: 97 96. Largest buds with more than 4 scales: 99 97. Buds with 1 scale: willows, Salix spp. (key to species on p. 53) 97. Buds with 3 or 4 scales: 98 98. Buds somewhat triangle-shaped, about 1/8 inch long, flattened closely to side of twig; pith intermittently chambered: hackberry, Celtis occidentalis 98. Buds ovoid, 3/16 to 1/4 inch long; pith continuous; spur shoots often present: birches, Betula spp. (See couplet 47 for key to species.)

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52 i d e n t i f y i n g i o w a ’ s t r e e s 99. Lateral buds of 2 distinct kinds: tiny 2-scaled buds near the end of the twig and much larger, stalked, many-scaled buds closer to the base of the twig: redbud, Cercis canadensis 99. Lateral buds not of 2 distinct kinds as described above: 100 100. Buds with about 6 scales, sometimes collateral (in pairs above the leaf scars, one beside the other); twigs about as wide as the buds or wider, often thorntipped: American plum, Prunus americana 100. Buds with 6 to 12 scales; twigs very slender, often narrower than the buds: 101

fig. 36 101. Bud scales spirally arranged, often marked with fine vertical lines (seen with magnifying glass) (fig. 36); trunk bark gray or brown, separating into vertical rows of small, rectangular plates when trees are several inches in diameter: ironwood or hop hornbeam, Ostrya virginiana 101. Bud scales arranged in 4 rows, not marked with fine lines;

trunk having a distinct twisted or muscle-bound appearance with smooth pale gray bark: American hornbeam, Carpinus caroliniana 102. Buds with many scales usually arranged in vertical rows (fig. 33); each leaf scar with many bundle scars; dried leaves from previous growing season sometimes persisting in large numbers: oaks, Quercus spp. (key to species on p. 54) 102. Without the above combination of characteristics: 103 103. Buds with 1 scale; stipule scars forming a fine line from one side of leaf scar completely around twig to other side: saucer magnolia, Magnolia ×soulangeana 103. Buds with 2 or more overlapping scales: 104 104. Buds globose to subglobose with rounded or blunt tips and thick red, glabrous scales: hawthorns, Crataegus spp. 104. Buds ovoid to ovoid-elongate with pointed tips, either hairy or glabrous: 105 105. Lowermost scale of each lateral bud centered directly over leaf scar (fig. 35a): poplars, Populus spp. (key to species on p. 54) 105. Lowermost scale of each lateral bud offset to one side of leaf scar (fig. 35b): 106

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106. Buds with several glabrous scales; freshly bruised twigs with a strong, unpleasant odor: 107 106. Buds with 2 to several scales that are bristle-tipped and/or hairy; twigs lacking the odor described above: apples, crabapples, and pears, Malus and Pyrus spp. 107. Bud scales red or reddish: black cherry, Prunus serotina 107. Bud scales brown with gray margins: chokecherry, Prunus virginiana

Key to Willows (Salix) Willows, which are difficult to identify when leaves and flowers are available, are especially troublesome to distinguish in winter. The following key distinguishes typical representatives of the most common species. 1. Tree with long yellow, drooping branches that often reach or nearly reach the ground: golden weeping willow, S. ×sepulcralis 1. Tree or large shrub; branches not long and drooping: 2 2. Buds 3/16 to 3/8 inch long, rather plump, opening to silky white catkins in late winter: 3 2. Buds 1/16 to 3/16 inch long; twigs very slender: 5 3. Native; buds often blackish: pussy willow, S. discolor 3. Cultivated; buds usually brown or reddish: 4

4. Twigs and branchlets densely gray-hairy: gray willow, S. cinerea 4. Twigs and branchlets glabrous or partly hairy, often glossy: goat willow, S. caprea 5. Small native tree with pole-like stems and upright branches, forming thickets in floodplains and other moist, low-lying areas; twigs usually reddish brown or orangebrown: sandbar willow, S. interior 5. Medium- to large-size tree with spreading branches; twigs brown, greenish brown, gray, or yellowish (sometimes tinged with red on one side): 6 6. Bud scale with freely overlapping edges on back (twig) side of bud (seen with magnifying glass); native tree: 7 6. Bud scale fused into a caplike structure with no visible edges; tree cultivated or wild: white willow, S. alba; crack willow, S. fragi­ lis; and their hybrids 7. Twigs brown or gray-brown with brown buds: black willow, S. nigra 7. Twigs light yellow or yellowish gray; buds brown or yellow, sometimes black on upper half: peachleaf willow, S. amygdaloides

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54 i d e n t i f y i n g i o w a ’ s t r e e s

Key to Poplars (Populus)

Key to Oaks (Quercus)

1. Twigs coated with white felt-like material that can be easily rubbed off: white poplar, P. alba 1. Twigs without such coating: 2 2. Twigs gray, gray-green, or yellow; glabrous: eastern cottonwood, P. deltoides 2. Twigs brown (sometimes with grayish cast due to covering of fine gray hairs): 3 3. Buds shiny dark brown, glabrous; lateral buds usually appressed to twigs: quaking aspen, P. tremuloides 3. Buds light brown, more or less covered with fine gray hairs; lateral buds diverging from twig at acute angle: bigtooth aspen, P. grandidentata

Oaks are difficult to identify in winter using characteristics of the twigs alone. The following key, which is based primarily on characteristics of the bark and acorns, will identify trees beyond the sapling stage. 1. Shell of acorn glabrous on inner surface; bark of branches either dark and prominently furrowed or light ashy gray and scaly (white oaks): 2 1. Shell of acorn hairy on inner surface; bark remaining smooth or only slightly roughened until branches are several inches in diameter, then becoming shallowly furrowed (red oaks): 5 2. Acorn-cup with a conspicuous fringe of soft bristles around rim; buds and twigs more or less covered with fine grayish hairs; corky outgrowths often present on branchlets: bur oak, Q. macrocarpa 2. Acorn-cup lacking fringe of bristles; buds and twigs glabrous to slightly hairy; branchlets lacking corky outgrowths: 3 3. Acorn-cup on stalk 1 to 4 inches long; tree native in moist, lowlying woods: swamp white oak, Q. bicolor 3. Acorn-cup unstalked or very short-stalked; tree native in upland woods: 4

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w i n t e r k e y s t o i o w a ’ s t r e e s 55

4. Acorn-cup with thick, warty scales; dried, lobed leaves often persisting in large numbers, especially on lower branches of tree: white oak, Q. alba 4. Acorn-cup with thin scales; dried leaves not normally persisting in winter: chinkapin oak, Q. muhlenbergii 5. Scales at top of acorn-cup loose, forming fringe around rim of cup; buds 1/4 to 1/2 inch long, densely hairy: black oak, Q. velutina 5. Scales of acorn-cup tightly appressed to cup; buds mostly 1/16 to 1/4 inch long, glabrous to partly hairy: 6

a fig. 37

b

c

6. Acorn-cup bowl-shaped or coneshaped, covering lower 1/3 to 1/2 of nut (fig. 37a, c): 8 6. Acorn-cup saucer-shaped, covering only base of nut (fig. 37b): 7 7. Acorn 5/8 to 1 inch long; buds mostly 3/16 to 1/4 inch long: red oak, Q. rubra 7. Acorn 3/8 to 1/2 inch long; buds about 1/8 inch long: pin oak, Q. palustris

8. Acorn 1 1/2 to 2 times longer than wide with cone-shaped cup (fig. 37a): Hill’s oak or northern pin oak, Q. ellipsoidalis 8. Acorn only slightly longer than wide with bowl-shaped cup (fig. 37c): 9 9. Buds 1/8 to 3/16 inch long; leaves not lobed: shingle oak, Q. imbricaria 9. Buds 3/16 to 1/4 inch long; leaves lobed: red oak, Q. rubra

Key to Elms (Ulmus) 1. Buds of 2 distinct types and sizes as follows: leaf buds less than 1/8 inch long near the tips of the twigs and globose flower buds 1/8 to 3/16 inch long closer to the bases of the twigs: Siberian elm, U. pumila 1. Buds larger than described above: 2 2. Bud scales red-brown with dark margins, glabrous or nearly so; twigs brown or reddish brown: American elm, U. americana 2. Buds dark purple or purplebrown, usually covered with shiny, copper-colored hairs, especially toward the tip; twigs gray: slippery elm, U. rubra

Key to Maples (Acer) 1. Terminal bud with 10 to 18 visible scales: sugar and black maples, A. saccharum and A. nigrum 1. Terminal bud with 2 to 6 visible scales: 2

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56 i d e n t i f y i n g i o w a ’ s t r e e s 2. Largest buds about 1/16 inch long, terminal frequently absent; small, shrubby, cultivated tree: Amur maple, A. ginnala 2. Largest buds 1/8 to 1/4 inch long; a tree, cultivated or native: 3 3. Buds white-hairy; twigs usually green or purple, often coated with white waxy material; fruits sometimes persisting on twigs in large numbers: boxelder, A. negundo 3. Buds glabrous or hairy along edges of scales only; twigs red or brown; fruits not persisting on twigs in large numbers: 4

a fig. 38

b

4. Opposing leaf scars touching at edges (fig. 38a); twigs brown; buds often at least partly green: Norway maple, A. platanoides 4. Opposing leaf scars not normally touching, though sometimes connected by a fine line (fig. 38b); twigs red or red-brown; buds red: silver maple, A. saccharinum

Key to Ashes (Fraxinus) Ashes are highly variable in their characteristics and not easy to distinguish in winter. The following key will identify typical specimens.

1. Buds usually black (sometimes brown on small saplings), the terminal raised above the uppermost laterals; twigs very stout with leaf scars rounded or elliptical in shape; wing of fruit extending to base of flattened and rather indistinct seed cavity: black ash, F. nigra 1. Buds light to dark brown, the terminal at the same level as the uppermost laterals; twigs moderate in diameter with leaf scars usually half-round in shape; wing of fruit extending no further than upper half of seed cavity: 2

a fig. 39

b



a b fig. 40

2. Lateral buds positioned in V-shaped notches in upper margins of leaf scars (fig. 39a); wing of fruit not extending along edge of seed cavity (fig. 40b); tree native in upland woods, often cultivated: white ash, F. americana 2. Lateral buds positioned immediately above leaf scars, which are straight or curved at top (fig. 39b); wing of fruit extending along upper part of seed cavity (fig. 40a); tree native in low-lying woods and widely cultivated: green ash, F. pennsylvanica

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Descriptions of  Tree Species Iowa’s tr ees a r e illustrated and described in the following pages. All native trees are included, except some rarities and the less common kinds of willows and hawthorns. Species from other parts of the United States, Europe, and Asia are included if they are commonly planted here. One species is illustrated and described on each set of  facing pages. Illustrations include leaves, buds, winter twigs, flowers, fruits, and, where it is especially distinctive, bark. The text includes a description of the species, notes on how to distinguish it from similar trees, and a description of its geographical distribution in Iowa. Also included are references to part 2, where there is information about the ecology, uses, and culture of the species. To make identification easier, the trees are arranged in seven groups based on similarities among leaves; colored tabs provide additional guidance.

• Leaves needlelike or scale-like, seeds in cones: pages 58–93 Leaves compound • Leaves opposite: pages 94–105 • Leaves alternate: pages 106–133 Leaves simple, lobed • Leaves opposite: pages 134–145 • Leaves alternate: pages 146–183 Leaves simple, not lobed • Leaf margins toothed: pages 184–243 • Leaf margins entire (not toothed): pages 244–263

To identify an unknown tree, first select the group to which it belongs. Next, page through that group, examining the illustrations until you find a match. If you don’t find a match or are not sure, refer to the keys on pages 16 to 56, which include some species not illustrated. Be sure to confirm your identification by reading the description on the page and comparing it to the tree.

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Eastern White Pine, Pinus strobus L. Distinguishing ch a r acter istics: Leaves in bundles of 5, very slender, 2 to 5 (usually about 3) inches long, marked with fine white lines (seen with magnifying glass), very flexible. Cones elongate, 4 to 5 (rarely to 8) inches long; scales without prickles. Bark dark gray to nearly black with flat plates separated by shallow fissures; eventually dark and deeply furrowed with scaly, blocky plates. Simila r tr ees: No other pine commonly planted in Iowa has leaves in bundles of 5. Iowa distr ibution: Native in northeastern Iowa and along Pine Creek in Muscatine County and the Iowa River in Hardin County, growing on bluffs, ridges, and wooded slopes, usually in well-drained soils. Planted throughout the state.

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Red Pine, Pinus resinosa Ait. Distinguishing ch a r acter istics: Leaves in bundles of 2, slender, 4 to 6 inches long, fairly flexible but breaking readily when bent in two. Cones 1 1/2 to 2 1/4 inches long; basal scales remaining on the twig when the cone falls, leaving a small depression in the base of the cone; scales without prickles. Bark divided into flat plates separated by shallow furrows and covered with red-orange scales. Simila r tr ees: Austrian pine has strongly whitened buds and larger cones that retain their basal scales when falling from the twigs. Ponderosa pine has some bundles with 3 needles and much larger cones with sharp prickles. Iowa distr ibution: Planted throughout the state but not commonly so in the west.

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Austrian Pine, Pinus nigra Arnold Distinguishing ch a r acter istics: Leaves in bundles of 2, stout, 4 to 6 inches long, rather stiff but resisting breakage when bent in two. Buds coated with a white waxy substance. Cones 2 to 3 inches long, falling intact (i.e., basal scales not missing); scales with tiny deciduous prickles. Bark divided into large, dark gray plates, more or less covered with lighter-colored scales. Simila r tr ees: Red pine and ponderosa pine are the only other pines planted in Iowa that regularly have leaves more than 4 inches long. Red pine has brown buds and, when mature, reddish bark. Ponderosa pine has at least some bundles with 3 needles. Fallen cones of both species have missing basal scales. (Small Austrian pines sometimes have needles that are shorter than 4 inches. These trees might be mistaken for Scots pine, but Austrian pine has fat whitened buds and Scots pine has slim red-brown buds.) Iowa distr ibution: Planted throughout the state.

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Ponderosa Pine, Pinus ponderosa Laws. Distinguishing ch a r acter istics: Leaves in bundles of both 2 and 3, stout, 4 to 11 inches long, flexible. Cones 2 1/2 to 4 (or more) inches long; basal scales remaining on the twig when the cones fall, leaving a depression in the base of each cone; scales armed with sharp prickles near the end. Bark divided into large, flat plates, yellowish brown to reddish in color. Simila r tr ees: Red and Austrian pines have smaller cones and all leaves in bundles of 2. Iowa distr ibution: Occasionally planted throughout the state.

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Scots Pine, Pinus sylvestris L. Distinguishing ch a r acter istics: Leaves in bundles of 2, slender, 1 to 4 inches long, usually twisted and often marked with fine white lines (seen with magnifying glass). Cones 1 to 2 inches long, falling intact (i.e., basal scales not missing); end of scales raised and pyramidal (less commonly flattened), with or without tiny prickles. Bark scaly and light orange on larger branches and upper trunk, divided into large gray plates covered with orange scales on lower trunk. Simila r tr ees: Mugo pine is shrubby; other common two-needle pines have longer leaves. Mature Scots pines can be easily distinguished from other species by the orange bark of their upper trunk and limbs. Iowa distr ibution: Planted throughout the state.

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Mugo Pine, Pinus mugo Turra. Distinguishing ch a r acter istics: Leaves in fascicles of 2, moderately stout, 1 1/2 to 3 inches long. Cones 3/4 to 1 1/2 inches long, without prickles. Simila r tr ees: This shrubby pine is easily distinguished from other species by its small size, multistemmed habit, and small, roundish cones. Iowa distr ibution: Planted throughout the state.

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Norway Spruce, Picea abies (L.) Karst. Distinguishing ch a r acter istics: Leaves linear, four-sided, evergreen, 3/8 to 1 inch long, dark green, with woody, peglike bases that remain on the twig when the green portions fall, spirally arranged and extending from the twig in several directions. Twigs drooping, orange on new growth. Buds with recurved scales. Cones pendant, 4 to 6 inches long, their scales dull brown, rigid, with finely toothed margins. Bark thin, dark, scaly. Simila r tr ees: White and blue spruces have smaller cones, and the twigs are stiffly held, not drooping. Blue spruce has longer, more sharply pointed leaves that are usually (in cultivated trees) noticeably blue-green in color. White spruce has grayish twigs. Firs and Douglas-fir resemble spruces and are often confused with them but differ in having flattened leaves that lack woody, peglike bases. Fir cones are held upright on the branches and disintegrate at maturity; cones of Douglas-fir have protruding bracts. Iowa distr ibution: Planted throughout the state; occasionally naturalized on cool, moist slopes in northeastern Iowa.

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White Spruce, Picea glauca (Moench) Voss. Distinguishing ch a r acter istics: Leaves linear, four-sided, evergreen, 1/3 to 3/4 inch long, green or light blue-green, with woody, peglike bases that remain on the twig when the green portions fall, spirally arranged and extending from the twig in several directions. Twigs gray on new growth. Buds with recurved scales. Cones pendant, 1 to 2 1/2 inches long, their scales dull light brown, rigid, with entire, rounded margins. Bark thin, dark, scaly. Simila r tr ees: Norway and blue spruces have larger cones and orangeish twigs. See also firs and Douglas-fir in the discussion of Norway spruce. Iowa distr ibution: Planted throughout the state.

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Blue Spruce, Picea pungens Engelm. Distinguishing ch a r acter istics: Leaves linear, four-sided, evergreen, very sharp-pointed, 3/4 to 1 1/4 inches long, green or blue-green, with woody, peglike bases that remain on the twig when the green portions fall, spirally arranged and extending from the twig in several directions. Twigs orange on new growth. Buds with recurved scales. Cones pendant, 2 1/4 to 4 (usually 3 to 3 1/2) inches long, their scales light yellow-brown, shiny, very flexible, with irregularly toothed margins. Bark thin, dark, scaly. Simila r tr ees: Norway and white spruces have shorter, dark green leaves that are not so sharply pointed and dull brown cones. See also firs and Douglas- fir under the discussion of Norway spruce. Iowa distr ibution: Planted throughout the state.

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Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco Distinguishing ch a r acter istics: Leaves linear, flat, with short petioles, evergreen, 3/4 to 1 1/4 inches long, blue-green above and marked with two white lines below, spirally arranged and extending from the twig in all directions. Buds ovoid-elongate, pointed, 1/4 to 3/8 inch long, with brown or red-brown overlapping scales. Cones 2 to 3 inches long, pendant, falling intact, with three-pronged bracts protruding between the scales. Bark gray and scaly on young trees, eventually becoming red-brown and deeply furrowed. Simila r tr ees: Spruces have woody, peglike leaf bases that persist on the twigs when the leaves fall. Leaves of true firs lack petioles. None of these trees have large, sharp-pointed buds. Iowa distr ibution: Planted throughout the state.

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White or Concolor Fir,

Abies concolor (Gord. and Glend.) Lindl. Distinguishing ch a r acter istics: Leaves linear, flat, blunt, without petioles, evergreen, 3/4 to 3 (usually 1 1/2 to 2) inches long, usually blue-green on both surfaces, spirally arranged on the twig but often twisted at the base and appearing two-ranked. Buds 1/8 to 1/4 inch long, blunt or rounded at tip, their scales tightly overlapping with a waxy coating. Cones upright on branches, disintegrating when mature, 3 to 5 inches long, with the scales wider than long. Bark smooth, gray on young trees, eventually dark and furrowed. Simila r tr ees: Leaves of balsam fir are dark green above and usually shorter. Blue spruce has sharp-pointed leaves with peglike bases. Douglas-fir has long, pointed buds; its cones fall intact and have forklike bracts protruding between the scales. Iowa distr ibution: Planted throughout the state.

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Balsam Fir, Abies balsamea (L.) Mill. Distinguishing ch a r acter istics: Leaves linear, flat, blunt, without petioles, evergreen, 3/4 to 1 1/2 inches long, dark green above and marked with two white lines below, spirally arranged on the twig but often twisted at the base and appearing two-ranked. Buds 1/8 to 1/4 inch long, blunt or rounded at tip, with tightly overlapping scales. Cones upright on branches, disintegrating when mature, 2 to 4 inches long, with the scales longer than wide. Bark smooth and gray on young trees, separating into thin red-brown scales on large trees. Simila r tr ees: White fir has blue-green and (usually) longer leaves. Leaves of spruces and hemlock have woody, peglike bases that remain on the twig when the leaves fall; their cones hang down and fall intact. Hemlock leaves are shorter than those of balsam fir and are petioled. Fraser fir, occasionally planted in Iowa and used for Christmas trees, has long, forked bracts protruding between the cone scales. Iowa distr ibution: Native on steep, north-facing slopes in Allamakee, Clayton, Winneshiek, and Howard counties in northeastern Iowa. Occasionally planted elsewhere.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 83

Eastern Hemlock, Tsuga canadensis (L.) Carr. Distinguishing ch a r acter istics: Leaves linear, flat, with short petioles, evergreen, 1/3 to 1/2 inch long, dark green above and marked with two white lines below, spirally arranged but appearing two-ranked, with those on the upper side of the twig shorter, frequently upside down, and lying close to the twig, with woody, peglike bases that remain on the twig when the green portions fall. Buds about 1/16 inch long. Cones 1/2 to 3/4 inch long with thin, papery scales, falling intact. Bark gray and scaly, often with a reddish cast, eventually becoming deeply furrowed. Simila r tr ees: Balsam fir has longer leaves without petioles or woody bases. Its cones are larger, upright, and disintegrate when mature. Iowa distr ibution: Occasionally planted, especially in the eastern and central parts of the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 85

European Larch, Larix decidua Mill. Distinguishing ch a r acter istics: Leaves linear but very slender, without petioles, 3/4 to 1 1/4 inches long, deciduous, spirally arranged on twigs, tufted at ends of spur shoots on branchlets. Twigs long, slender, drooping. Terminal bud about 1/16 inch long with brown overlapping scales. Cones 3/4 to 1 1/2 inches long with 40 to 50 thin scales, held upright on the twigs and persisting for several years. Bark separating into irregular plates covered with gray and red-brown scales. Simila r tr ees: The closely related Tamarack or eastern larch (L. laricina) has cones 1/2 to 3/4 inch long with only 12 to 15 scales. Most other conifers are evergreen. Iowa distr ibution: Planted throughout the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 87

Baldcypress, Taxodium distichum (L.) Rich. Distinguishing ch a r acter istics: Leaves linear, flat, 1/4 to 3/4 inch long, green on both surfaces, spirally arranged but appearing two-ranked on green twigs. Leafy twigs deciduous in autumn. Buds small. Cones ball-shaped, 3/4 to 1 inch in diameter, with thick, woody scales. Bark gray or red-brown, dividing into flat ridges separated by shallow furrows. Simila r tr ees: Larches, which are also deciduous, have longer leaves that are tufted at the ends of spur shoots and thin-scaled cones. Baldcypress leaves turn orange-brown in autumn, while larches turn yellow. Iowa distr ibution: Cultivated.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 89

Yews, Taxus L. Distinguishing ch a r acter istics: Small trees or large shrubs. Leaves linear, flat, evergreen, dark green above and light green below with a short, twisted petiole, spirally arranged but appearing two-ranked. Buds small. Seeds green to black, seated in bright red fleshy cups, solitary in the leaf axils. Plants dioecious. Bark brown to reddish brown, scaly or shaggy. Simila r tr ees: Easily distinguished from other conifers with similar leaves by their shrubby habit and size. The leaves are light green beneath, while those of hemlock, firs, and Douglas-fir are bluish green or white. The yews’ unique seeds, when present, also distinguish them from other conifers. Iowa distr ibution: Cultivated throughout the state. One species, T. canadensis, is native on rocky bluffs and moist wooded slopes in eastern Iowa.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 91

Eastern Redcedar, Juniperus virginiana L. Distinguishing ch a r acter istics: Leaves evergreen, of two types, both usually (but not always) present on the same tree: (1) scale-like, opposite, dull-pointed, closely appressed to twig, about 1/16 inch long, each pair over­ lapping the pair immediately above it and oriented at right angles to it, and (2) needlelike, opposite or occasionally in whorls of three, sharp-pointed, divergent from twig, 1/4 to 1/2 inch long. Foliage with a dark green, blue-green, or reddish cast. Twigs with scale leaves four-sided. Buds tiny, naked, hidden by leaves. Cones blue, berrylike, 1/4 to 1/3 inch in diameter; trees dioecious. Bark light gray or red-brown, separating into long, narrow, vertically oriented strips. Simila r tr ees: Arborvitae has light green, scale-like leaves, flattened branchlets, and small, woody cones. Other, low-growing junipers are native in northeastern Iowa, and some other juniper species are planted. Iowa distr ibution: Native and planted throughout the state.

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d e s c r i p t i o n s o f t r e e s p e c i e s 93

Arborvitae or Northern White Cedar, Thuja occidentalis L.

Distinguishing ch a r acter istics: Leaves scale-like, opposite, evergreen, closely appressed to the side of the twig, light green in color, about 1/8 (occasionally up to 1/4) inch long; leaf pairs alternating at right angles with the members of each lateral pair folded in half and tightly overlapping the flattened facial pair immediately above them. Twigs and branchlets decidedly flattened. Buds naked, tiny. Cones erect, 1/3 to 1/2 inch long; scales 8 to 12, of which only 4 bear seeds. Bark gray to red-brown, shreddy, with shallow furrows and interconnecting ridges. Simila r tr ees: Eastern redcedar has four-sided twigs, berrylike cones, and at least some needlelike leaves. Its leaves are also darker than arborvitae. Iowa distr ibution: Planted throughout the state, rarely naturalized on cliffs in northeast Iowa.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 95

Boxelder, Acer negundo L. Distinguishing ch a r acter istics: Leaves once-pinnately compound, opposite; leaflets 3 to 9 in number (usually 3 or 5), ovate, sometimes shallowly lobed, 2 to 4 inches long, the margins entire or coarsely and shallowly toothed. Winter twigs moderate in diameter, green or purple, usually coated with a white waxy substance; leaf scars V-shaped with 3 bundle scars, opposing leaf scars joined at their ends and thus encircling the twigs, the junction prolonged upward into a short point on each side of the twig. Buds ovoid, densely white-hairy, 1/8 to 1/4 inch long with 2 or 4 visible scales. Flowers very small, greenish, dioecious, apetalous, appearing just before the leaves in spring; staminate long-stalked in umbellike clusters; pistillate in racemes. Fruit a pair of samaras joined at the base; wings 1 to 2 inches long, drooping; samaras ripening in autumn, often remaining on the tree through winter. Bark gray or brown, furrowed with scaly ridges. Simila r tr ees: Ashes, the only other common trees with opposite, pinnately compound leaves, have 7 to 11 leaflets and single, paddle-shaped sam­ aras. Easily distinguished from other maples and ashes in winter by its greenish or purple twigs, white-hairy buds, and upward-pointing leaf scar junctions. Iowa distr ibution: Native throughout the state, occasionally cultivated.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 97

Green Ash, Fraxinus pennsylvanica Marsh. Distinguishing ch a r acter istics: Leaves once-pinnately compound, opposite, 10 to 12 inches long; leaflets 5 to 9 in number (usually 7), oblong-lanceolate or less commonly elliptic, 2 to 6 inches long, tapering at the base and extending along the upper side of their 1/16- to 3/16-inch-long stalks; margins conspicuously toothed; upper surface dark green and often glossy; lower surface light green, glabrous or nearly so (hairy in the form called red ash). Winter twigs moderate in diameter, gray, glabrous (finely hairy in the form called red ash); leaf scars small, half-round to nearly round, bundle scars numerous and very close together, forming a fine curved line. Buds globose to subglobose, brown, with 1 or 2 pairs of visible scales, the terminal 1/8 to 1/4 inch long. Flowers very small, dioecious, apetalous, appearing with or before leaves; staminate in short, compact panicles, pistillate in open panicles. Fruit a narrow, paddle-shaped samara 1 to 2 inches long that often persists in winter; wing extending along upper half of seed cavity. Bark ashy gray or gray-brown, furrowed, with narrow, interconnecting ridges enclosing diamond-shaped spaces. Simila r tr ees: White ash has relatively broad leaflets with entire or obscurely toothed margins and stalks about 1/4 inch long; the wing of its samara does not extend along the sides of the seed cavity. Black ash has 9 to 11 unstalked leaflets and its fruits have indistinct, flattened seed cavities. Iowa distr ibution: Native and planted throughout the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 99

White Ash, Fraxinus americana L. Distinguishing ch a r acter istics: Leaves once-pinnately compound, opposite, 8 to 12 inches long; leaflets 5 to 9 in number (usually 7), ovatelanceolate to oval, 2 to 6 inches long with stalks 3/16 to 1/2 inch long; margins entire or obscurely toothed (rarely with conspicuous teeth); upper surface dark green and sometimes glossy, lower surface light green or very pale, glabrous. Winter twigs moderate in diameter, gray or brown, glabrous; leaf scars small, half-round to nearly round, with a conspicuous V-shaped notch in the top, bundle scars numerous and very close together, forming a fine curved line. Buds and flowers similar to green ash. Fruit a paddle-shaped samara 1 to 2 inches long, often persisting into winter; wing not extending along seed cavity. Bark similar to green ash. Simila r tr ees: Green and black ash have shorter-stalked or unstalked leaflets with finely toothed margins. Iowa distr ibution: Native as far west as the Cedar River in northern Iowa, the Des Moines River and its principal tributaries in the central part of the state, and the Missouri River in southern Iowa. Planted throughout the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 101

Black Ash, Fraxinus nigra Marsh. Distinguishing ch a r acter istics: Leaves pinnately compound, opposite, 12 to 16 inches long; leaflets 7 to 13 in number (usually 9 to 11), oblonglanceolate, 3 to 6 inches long, not stalked, conspicuously toothed, glabrous except for tufts of orange-brown hairs where they join the leaf stem. Winter twigs moderate to stout, gray, glabrous; leaf scars half-round to nearly round; bundle scars numerous and close together, forming a fine curved line. Buds similar to green ash but usually black. Flowers very small, polygamous or dioecious, apetalous, appearing with or before the leaves in spring; staminate in short, compact panicles, pistillate in open panicles. Fruit a paddle-shaped samara 1 to 1 1/2 inches long, often persisting in winter; wing notched at apex, surrounding the flat, indistinct seed cavity. Bark gray, scaly, becoming shallowly and rather indistinctly furrowed on large trees. Simila r tr ees: Green and white ash have stalked leaflets, brown buds, and samaras with distinct seed cavities that are rounded in cross section. Iowa distr ibution: Native as far west as the Des Moines River valley. Not commonly planted.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 103

Ohio Buckeye, Aesculus glabra Willd. Distinguishing ch a r acter istics: Leaves palmately compound, opposite; leaflets 5 to 7 in number (usually 5), 3 to 6 inches long, elliptic to slightly oblong, gradually tapered to both the apex and the base; margins finely toothed. Winter twigs stout, red-brown to gray, glabrous; leaf scars rather large, half-round to shield-shaped, bundle scars 3 or in 3 groups. Buds ovoid, light brown, with 5 or 6 pairs of dry brown scales, the terminal 1/2 to 2/3 inch long. Flowers yellow-green, perfect or imperfect, irregular, in panicles, appearing after the leaves in spring. Fruit a nutlike capsule 1 to 2 inches in diameter with 1 or 2 seeds; capsule wall thick and leathery with deciduous prickles; seeds large, dark shiny brown, with a single large, pale spot (hilum). Bark ashy gray, separating into scaly plates divided by shallow furrows. Simila r tr ees: Common horsechestnut, our only other tree with palmately compound leaves, has white flowers and obovate, coarsely toothed leaflets abruptly tapered to the apex. Several shrubby species of Aesculus are planted. In winter, horsechestnut has dark, sticky buds. Iowa distr ibution: Native south of a line extending from Mills County northeast to Boone County east to Clinton County. Planted throughout the state and sometimes escaping.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 105

Common Horsechestnut, Aesculus hippocastanum L. Distinguishing ch a r acter istics: Leaves palmately compound, opposite; leaflets 5 to 7 in number (usually 7), 4 to 8 inches long, strongly obovate, abruptly tapered to the apex; margins coarsely toothed. Winter twigs stout, red-brown to gray-brown, glabrous; leaf scars large, triangular or shieldshaped, with 3 to 9 bundle scars. Buds ovoid, sticky, with 4 to 6 pairs of large scales, the terminal 1/2 to 1 inch. Flowers white streaked with red or yellow, perfect or imperfect, irregular, in showy panicles, appearing after the leaves in spring. Fruit a nutlike capsule about 2 inches in diameter with 1 to 3 seeds; capsule wall thick, leathery, and prickly; seeds large, dark shiny brown with a single large, pale spot (hilum). Bark gray, scaly. Simila r tr ees: Ohio buckeye has elliptic to oblong, finely toothed leaflets gradually tapered to the apex, yellow-green flowers, and light brown nonsticky buds. Iowa distr ibution: Occasionally planted.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 107

Black Walnut, Juglans nigra L. Distinguishing ch a r acter istics: Leaves once-pinnately compound, alternate, 1 to 2 feet long, usually tipped by a pair of leaflets smaller than those near the middle of the leaf; leaflets 11 to 23 in number, ovatelanceolate, 2 1/2 to 4 inches long, finely toothed, glabrous above and hairy below. Winter twigs moderate to rather stout, gray-green or light brown; pith chambered; leaf scars large, heart-shaped, with 3 bundle scars. Buds globose to subglobose with 2 or 4 visible scales covered with tiny gray hairs, the terminal bud 3/16 to 1/3 inch long. Flowers monoecious, appearing with or shortly after the leaves in spring, the staminate in catkins and the pistillate in short spikes. Fruit a round nut 1 1/2 to 2 inches in diameter with a hard, corrugated shell encased in a green, indehiscent, semifleshy husk that eventually turns black. Bark dark gray or black, deeply furrowed, with interconnecting ridges that become thick and blocky on large trees. Simila r tr ees: Butternut is the only other tree having the combination of compound leaves, chambered pith, and true terminal buds. It has long yellowish terminal buds, a conspicuous fringe of hairs along the top of each leaf scar, oblong fruits, and light gray bark. Its leaves end in a single leaflet. Iowa distr ibution: Native and planted throughout the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 109

Butternut, Juglans cinerea L. Distinguishing ch a r acter istics: Leaves once-pinnately compound, alternate, 1 to 2 1/2 feet long, usually tipped by a single leaflet equal to the others in size; leaflets 11 to 17 in number, oblong-lanceolate, 2 to 4 inches long, finely toothed, hairy below. Winter twigs moderate to rather stout, green or red-brown; pith chambered; leaf scars large, lobed, each with 3 bundle scars and a fringe of yellow-brown hairs along its upper margin. Buds with 2 or 4 visible scales covered with tiny, usually yellow-brown hairs; the terminal bud ovoid-elongate, 3/8 to 3/4 inch long, much larger than the globose lateral buds. Flowers similar to black walnut. Fruit similar to black walnut but decidedly oblong in shape. Bark smooth on young trees, eventually furrowed with broad, flat, ashy gray ridges. Simila r tr ees: Black walnut has round nuts, squat gray buds, and no fringe of hairs along the top of its leaf scars. Iowa distr ibution: Native as far west as the Des Moines River and its principal tributaries and in scattered localities in the southwestern part of the state. Not commonly planted.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 111

Shagbark Hickory, Carya ovata (Mill.) K. Koch Distinguishing ch a r acter istics: Leaves once-pinnately compound, alternate, 8 to 14 inches long; leaflets 5 in number (occasionally 7), finely toothed, glabrous, the terminal 3 leaflets 4 to 7 inches long and the other 2 smaller. Winter twigs moderate to rather stout, red-brown or dark gray-green; leaf scars large, half-round to heart-shaped, with numerous bundle scars. Terminal buds ovoid, 1/2 to 3/4 inch long; outer bud scales dark brown and nearly glabrous, inner scales yellow-brown and finely hairy. Flowers monoecious, appearing when the leaves are nearly full-grown in spring, the staminate in branched catkins and the pistillate in short spikes. Fruit a nut about 1 1/2 inches long; husk 1/8 to 1/2 inch thick, splitting completely open at maturity. Bark slate gray, smooth on young trees, eventually dividing into irregularly shaped, vertically oriented strips that curve away from the trunk at one or both ends, giving the tree a shaggy appearance. Simila r tr ees: Other trees with alternate, once-pinnately compound leaves have more than 5 leaflets. In winter, shellbark hickory has similar bark but its twigs are pale orange. Iowa distr ibution: Native as far west as the Des Moines and Raccoon rivers in central Iowa and the Missouri River in southern Iowa, but only locally common along the western edge of this range. There are old reports from the natural lakes in Dickinson County. Not commonly planted.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 113

Shellbark Hickory, Carya laciniosa (Michx. f.) Loud. Distinguishing ch a r acter istics: Leaves once-pinnately compound, alternate, 15 to 22 inches long; leaflets 7 (sometimes 5 or 9), glabrous above and finely soft-hairy below, the terminal 3 leaflets 4 to 9 inches long and the others smaller. Winter twigs pale orange-brown, otherwise similar to shagbark hickory. Terminal buds ovoid, 1/2 to 1 inch long (usually about 3/4 inch); scales loose, the inner covered with pale yellow-brown hairs and the outer dark brown. Flowers similar to shagbark hickory. Fruit a nut 1 3/4 to 2 1/2 inches long; husk 1/4 to 1/2 inch thick, splitting completely open. Bark slate gray, shaggy. Simila r tr ees: Shagbark hickory has 5 leaflets and smaller nuts. Iowa distr ibution: Native along the Mississippi River and its principal tributaries north to Jackson and Iowa counties and locally in south central Iowa. Not commonly planted.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 115

Mockernut Hickory, Carya tomentosa Nutt. Distinguishing ch a r acter istics: Leaves once-pinnately compound, alternate, 9 to 14 inches long; leaflets mostly 7 to 9, soft-hairy below, the terminal 3 leaflets 3 to 6 inches long and the others smaller. Winter twigs red-brown, hairy; leaf scars similar to shagbark hickory. Terminal buds subglobose, 3/8 to 3/4 inch long; inner scales densely covered with fine yellowbrown hairs; outer scales dark red-brown, deciduous in late autumn. Flowers similar to shagbark hickory. Fruit a nut 1 1/2 to 2 inches long; husk 1/8 to 1/4 inch thick, splitting nearly to the base. Bark dark gray, shallowly furrowed with interconnecting ridges. Simila r tr ees: Shagbark hickory has 5 leaflets and shaggy bark; bitternut hickory has slender bright yellow buds. Iowa distr ibution: Native from Lee County north to Scott, Cedar, and Wapello counties. Not commonly planted.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 117

Bitternut Hickory, Carya cordiformis (Wangenh.) K. Koch Distinguishing ch a r acter istics: Leaves once-pinnately compound, alternate, 6 to 10 inches long; leaflets 7 to 11 in number, glabrous above and either glabrous or hairy below, finely toothed, the terminal leaflet 3 to 6 inches long and the others slightly smaller. Winter twigs slender to moderate in diameter, gray-green or gray-brown; leaf scars moderately large, half-round to heart-shaped, with numerous bundle scars. Terminal buds ovoid-elongate with 2 bright yellow scales that meet along their edges without overlapping, 1/3 to 3/4 inch long. Flowers similar to shagbark hickory. Fruit a nut about 1 inch long; husk winged above the middle, less than 1/8 inch thick, splitting halfway open at maturity. Bark light gray, smooth on young trees, eventually very shallowly furrowed with narrow interconnecting ridges. Simila r tr ees: The bright yellow buds of this species are distinctive. Iowa distr ibution: Native as far west as the valleys of the Missouri and Little Sioux rivers; also present in woods around the Spirit-Okoboji lakes chain and along the Big Sioux River north to Plymouth County. Not commonly planted.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 119

Pecan, Carya illinoensis (Wangenh.) K. Koch Distinguishing ch a r acter istics: Leaves once-pinnately compound, alternate, 12 to 20 inches long; leaflets 9 to 17, prominently curved, glabrous or nearly so, 4 to 8 inches long, the terminal the same size as the laterals. Winter twigs brown or red-brown; leaf scars similar to bitternut hickory. Terminal bud ovoid, 1/4 to 1/2 inch long; scales meeting at the edges without overlapping, brown or yellow-brown. Flowers similar to shagbark hickory. Fruit a nut 1 to 2 1/2 inches long; husk winged, very thin, splitting to the base. Bark light brown or reddish brown; divided into irregular, scaly ridges and narrow furrows. Simila r tr ees: Other hickories have fewer leaflets that are not so strikingly curved. Iowa distr ibution: Native along the Mississippi River as far north as Jackson County. Occasionally planted.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 121

European Mountain-ash,

Sorbus aucuparia L. [Pyrus aucuparia (L.) Gaertn.] Distinguishing ch a r acter istics: Leaves once-pinnately compound, alternate; leaflets usually 13 or 15 in number (rarely 9, 11, or 17), 1 to 2 1/4 inches long, oblong with a blunt or acute tip, toothed, persistently hairy beneath. Winter twigs moderate in diameter, glabrous, gray or reddish brown; leaf scars linear or crescent-shaped, raised, each with 5 (rarely 3 or 7) bundle scars. Buds ovoid with dark reddish purple scales, the terminal 3/8 to 3/4 inch long and more or less covered with pale hairs, much larger than the laterals. Flowers white, perfect, in showy corymblike clusters, appearing after the leaves in late spring. Fruit a pome about 3/8 inch in diameter, bright red or orange when ripe. Bark smooth and bronze-colored on young trees, becoming gray and slightly roughened on older trees. Simila r tr ees: Other trees having alternate, pinnately compound leaves and toothed leaflets have much larger leaflets. In winter, other trees having large, hairy terminal buds with more than one scale have larger and more conspicuous leaf scars. Iowa distr ibution: Cultivated throughout the state and occasionally escaping to the wild in northeast Iowa.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 123

Staghorn Sumac, Rhus typhina L. Distinguishing ch a r acter istics: Leaves once-pinnately compound, alternate, 16 to 24 inches long; leaflets 11 to 31 in number, 2 to 5 inches long, oblong-lanceolate, sharply toothed (deeply lobed in some cultivars), nearly glabrous; petioles hairy. Winter twigs stout with thick pith, densely covered with brown velvety hairs; leaf scars ringlike, nearly encircling the buds, each with 3 to 9 bundle scars. Buds more or less cone-shaped, 1/8 to 3/16 inch long, the scales obscured by a dense covering of golden-brown hairs; the terminal bud absent. Flowers very small, yellow-green, perfect or imperfect, in dense panicles, appearing in early summer. Fruit a red hairy drupe about 3/16 inch in diameter borne in compact, upright clusters 3 to 5 inches long that persist through winter. Bark smooth, gray, with prominent orange lenticels, becoming scaly on larger stems. Simila r tr ees: Walnuts have similar leaves but can be distinguished by their chambered pith, true terminal buds, and large, lobed leaf scars. Tree-ofheaven has entire leaflets and large, shield-shaped leaf scars. Iowa distr ibution: Native from Allamakee and Winneshiek counties south to Clinton and Jones counties and in scattered locales in the north central part of the state. Also reported from Iowa County. Cultivars with dissected leaves are sometimes planted.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 125

Tree-of-heaven, Ailanthus altissima (Mill.) Swingle Distinguishing ch a r acter istics: Leaves once-pinnately compound, alternate, 1 1/2 to 4 feet long; leaflets 9 to 41 in number, 3 to 6 inches long, ovate-lanceolate; margins entire except for 1 or 2 gland-tipped teeth near base; surfaces glabrous. Winter twigs stout, light brown, with thick, light orange-brown pith; leaf scars large and shield-shaped with about 9 bundle scars. Buds dome-shaped, 1/8 to 3/16 inch long, with 2 or 4 red-brown scales covered with pale hairs; the terminal bud absent. Flowers yellow-green, dioecious or less commonly perfect, in panicles, appearing in early summer. Fruit a twisted, oblong samara 1 to 1 1/2 inches long with a single seed in the middle, persisting on the branches in winter. Bark smooth, gray with vertical white streaks, becoming slightly furrowed on large trees. Simila r tr ees: No other tree has entire leaflets with gland-tipped teeth at the base. In winter, Kentucky coffee tree and sumacs are the only other trees having stout twigs with no terminal buds. Coffee tree has mottled twigs, 3 or 5 bundle scars, and buds embedded within the twig. Sumacs have narrow leaf scars that nearly encircle their cone-shaped buds. Iowa distr ibution: Cultivated in towns and cities, especially in the southern half of the state, often escaping to vacant lots, roadsides, and other waste places.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 127

Prickly-ash, Zanthoxylum americanum Mill. Distinguishing ch a r acter istics: Colonial shrub or occasionally a small tree. Leaves once-pinnately compound, alternate, the leaf stems (rachises) often prickly; leaflets 7 to 11, ovate, not stalked, 3/4 to 2 1/2 inches long, dotted with tiny glands (seen against strong light), the margins minutely and distantly toothed. Winter twigs moderate in diameter, brown, armed with small paired spines; leaf scars 3-lobed with 3 bundle scars. Buds globose, 1/8 to 3/16 inch in diameter, red, with indistinct scales. Flowers tiny, greenish, dioecious, in small clusters, blooming in spring. Fruit a tiny red follicle with 1 or 2 shiny black seeds about 1/8 inch long that are suspended by slender stalks. Simila r tr ees: Black locust, the only other Iowa tree with paired spines, has stalked leaflets and inconspicuous buds that are not reddish. Iowa distr ibution: Native throughout the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 129

Black Locust, Robinia pseudoacacia L. Distinguishing ch a r acter istics: Leaves once-pinnately compound, alternate, 8 to 14 inches long; leaflets 7 to 21 in number, 1 1/2 to 2 inches long with stout stalks 1/8 to 1/4 inch long, ovate-oblong in shape, with entire margins and glabrous surfaces. Winter twigs moderate in diameter, prominently angled and zigzagged, light reddish brown, glabrous, with pairs of sharp stipular spines up to 1/2 inch long; leaf scars small, 3-lobed to broadly triangular, each with 3 bundle scars. Buds embedded in the leaf scars so apparently absent. Flowers white, perfect, irregular, in showy racemes, appearing in late spring or early summer. Fruit a flattened pod 2 to 4 inches long, abruptly tapered or rounded at ends, with 3 to 8 seeds about 3/16 inch long. Bark deeply furrowed with thick, elongate ridges, reddish brown to nearly black. Simila r tr ees: Prickly-ash is a shrub with paired spines and similar leaves that forms colonies like black locust. It can be distinguished as follows: leaflets not stalked, twigs straight and rounded, buds reddish and clearly visible in the axils of the leaves (above leaf scars in winter). Iowa distr ibution: Planted throughout most of the state and often naturalized or escaped from cultivation.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 131

Honey Locust, Gleditsia triacanthos L. Distinguishing ch a r acter istics: Leaves once- or twice-pinnately compound (both types usually present on same tree), alternate, 6 to 12 inches long; leaflets oblong, 1/2 to 1 1/2 inches long, with tiny, inconspicuous, widely spaced indentations. Winter twigs moderate in diameter, greenish or redbrown, glabrous and often glossy; those of wild trees commonly armed with smooth, stout, branched thorns; leaf scars small and irregularly shaped with 3 bundle scars. Buds brownish, embedded in the leaf scar and surface of the twig, with only their tips protruding; the terminal bud absent. Flowers small, greenish white, regular, perfect or imperfect, in racemes, appearing in early summer. Fruit a flattened and often twisted leathery pod 6 to 18 inches long with 12 or more seeds about 1/3 inch long. Bark of younger trees gray and separating into long, thin, flattened ridges slightly upturned at the end, becoming deeply furrowed and nearly black. Simila r tr ees: Kentucky coffee tree is the only other tree with twicecompound leaves; it has larger leaflets, much stouter twigs, and thick, woody pods. In winter, hawthorns are the only other trees with large, smooth thorns. Their thorns are relatively slender and unbranched (rarely branched on trunks). They also have reddish buds clearly visible on the surface of the twig. Iowa distr ibution: Commonly planted throughout the state and native across most of southern, eastern, and central Iowa.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 133

Kentucky Coffee Tree, Gymnocladus dioicus (L.) K. Koch Distinguishing ch a r acter istics: Leaves twice-pinnately compound, alternate, 1 to 3 feet long; leaflets 40 or more, 1 1/2 to 4 inches long, ovate, entire, glabrous. Winter twigs very stout, dark reddish brown mottled with gray, glabrous; pith very thick, orange; leaf scars large, heart-shaped with 3 or 5 bundle scars. Buds greenish or brown, sunken within small, craterlike depressions in the surface of the twig; the terminal bud absent. Flowers greenish white, dioecious, slightly irregular, in racemes, appearing in early summer. Fruit a thick, woody pod 4 to 6 inches long with 3 to 9 seeds 5/8 to 3/4 inch long, often persisting on the tree through winter. Bark on younger trees light gray and separating into thin, scaly ridges upturned on one edge; eventually somewhat darker and furrowed with short, scaly ridges or rows of small, scaly plates. Simila r tr ees: Honey locust is our only other tree with twice-pinnate leaves. It has smaller leaflets, relatively slender and often thorny twigs, and long, leathery, flattened, often twisted pods with smaller and more numerous seeds. In winter, tree-of-heaven is the only other species having stout twigs with large leaf scars and no terminal buds. It has 7 or more bundle scars and hairy buds exposed on the surface of the twig. Iowa distr ibution: Native in all regions of Iowa but not in all localities with suitable habitat. (See the discussion in part 2.) Occasionally planted.

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Sugar Maple, Acer saccharum Marsh. Distinguishing ch a r acter istics: Leaves simple, opposite, palmately 5-lobed with 1 or 2 pairs of large teeth per lobe, 3 to 6 inches long, glabrous, with acute-angled sinuses; petioles 1 1/2 to 4 inches long with watery sap; stipules not persisting. Winter twigs moderate in diameter, light brown to orange-brown, often with a pale waxy coating; leaf scars V-shaped with 3 bundle scars. Buds ovoid, sharp-pointed, dark brown to nearly black, glabrous or nearly so, the terminal 1/4 to 3/8 inch long with 10 to 18 visible scales, the laterals smaller and fewer-scaled. Flowers very small, greenish, perfect or imperfect, apetalous, long-stalked, in umbellike clusters, appearing just before the leaves in spring. Fruit a pair of samaras joined at the base; wings 1/2 to 1 inch long, parallel or slightly divergent; samaras ripening and falling in late summer or autumn. Bark dark gray, irregularly furrowed with thick, scaly ridges. Simila r tr ees: Norway maple has milky sap, tufts of hair in the vein axils on the lower surface of its leaves, fruits with widely divergent wings, and more shallowly furrowed bark with thin, interconnecting ridges. See also discussion of black maple in the next entry. In winter, not easily distinguished from black maple. Other trees with opposite leaf scars have terminal buds with only 2 to 6 visible scales. Iowa distr ibution: Native in the eastern part of the state and planted throughout.

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Black Maple,

Acer nigrum Michx f. [A. saccharum var. nigrum (Michx. f.) Loud.] Distinguishing ch a r acter istics: Resembling sugar maple except leaves have 3 lobes with few or no teeth, finely hairy beneath, with the 2 side lobes often drooping; angles between lobes 90 degrees or more; stipules often persisting. Simila r tr ees: Typical sugar maple has 5-lobed, prominently toothed, glabrous leaves with acute-angled sinuses, and its stipules do not persist. However, one can often find trees whose characteristics are intermediate between the two species and cannot be definitely identified as one or the other; see the discussion in part 2. Iowa distr ibution: Native in the eastern two-thirds to three-fourths of the state, but very local along the west edge of the range. Occasionally planted throughout.

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Norway Maple, Acer platanoides L. Distinguishing ch a r acter istics: Leaves simple, opposite, palmately 5-lobed (rarely 7), 2 1/2 to 6 inches long; margins of lobes entire or with 1 or 2 pairs of sharp teeth per lobe; surfaces glabrous except for tufts of hairs beneath in the vein axils; petioles 3 to 4 inches long with milky sap. Winter twigs moderate in diameter, brown or olive-brown; leaf scars small, V-shaped, with 3 bundle scars; opposing leaf scars touching at the ends, the pair thus encircling the twig. Buds subglobose, blunt-tipped, the terminal 3/16 to 1/3 inch long and the laterals smaller; bud scales 4 to 6, green turning to red or dark purple, glabrous or nearly so. Flowers yellow-green, perfect or imperfect, with petals, in corymbs, appearing just before the leaves in spring. Fruit a pair of samaras joined at the base; wings 1 1/2 to 2 inches long, spreading apart at an angle of 180 degrees; samaras ripening and falling from the tree in late summer or autumn. Bark gray, shallowly furrowed with narrow, interconnecting ridges enclosing diamond-shaped spaces. Simila r tr ees: Sugar and black maples have clear sap, apetalous flowers, fruits with nearly parallel wings, sharp-pointed terminal buds with 10 to 18 scales, and more deeply and irregularly furrowed bark. In winter, the large, fat, blunt terminal buds easily distinguish this species from other maples. Iowa distr ibution: Planted throughout the state.

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Silver Maple, Acer saccharinum L. Distinguishing ch a r acter istics: Leaves simple, opposite, palmately 5-lobed with deep, narrow sinuses, 3 to 7 inches long; margins of lobes toothed; surfaces glabrous, the lower very pale or whitened; petioles 2 to 4 inches long with watery sap. Winter twigs moderate to rather slender, dull red or light red-brown, glabrous; leaf scars V-shaped with 3 bundle scars, opposing leaf scars not touching but usually connected by a fine line. Buds ovoid (leaf buds) or globose (flower buds), bright red to dark reddish purple, 1/8 to 1/4 inch long, with 2 to 6 visible scales that are hairy along the edges; flower buds in conspicuous clumps. Flowers tiny, apetalous, red, hidden by the bud scales; functional stamens and pistils in different flowers, both types often present on the same tree, but one type often predominating. Fruit a pair of samaras joined at the base, one of which is often aborted; wing 1 1/2 to 2 inches long; samaras ripening and falling in late spring or early summer. Bark smooth, light gray on young trees, eventually separating into irregular rows of long, scaly, ashycolored plates. Simila r tr ees: Other large maples have more shallowly lobed leaves. In winter, flower buds of other common maples are neither clumped nor bright red, and their leaf scars touch at the tips. Iowa distr ibution: Native and planted throughout the state.

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Red Maple, Acer rubrum L. Distinguishing ch a r acter istics: Leaves simple, opposite, palmately 3- to 5-lobed with toothed margins, 2 to 6 inches long, glabrous; lower surface very pale or whitened. Winter twigs and buds similar to silver maple. Flowers reddish, with petals, otherwise similar to silver maple. Fruit ripening in late spring or early summer; wings 1/2 to 1 inch long, slightly divergent. Bark smooth and pale gray on young trees, eventually darker and similar to sugar maple. Simila r tr ees: Silver maple has more deeply lobed leaves with the central lobe widest near the middle; the central lobe of red maple leaves is widest at its base. Silver maple foliage is predominately yellow in autumn, while red maple is red and purple. Hybrids between the two species, with intermediate-shaped leaves and red fall color, can often be found in cultivation (see the discussion in part 2). Iowa distr ibution: Planted throughout the state, possibly native in Allamakee County.

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Amur Maple, Acer ginnala Maxim. Distinguishing ch a r acter istics: Small tree or large shrub. Leaves with 3 lobes, with the middle lobe much larger than the others, 1 to 3 inches long; margins toothed. Winter twigs slender, red or brown. Buds about 1/16 inch long, the terminal replaced by fruit clusters on some twigs; visible scales 4 or 6, light brown to red-brown, glabrous or hairy along the edges. Flowers yellowish white, in panicles, appearing after the leaves in late spring or early summer. Fruit ripening in late summer; wings about 1 inch long, slightly divergent. Simila r tr ees: Other maples have larger leaves whose lobes are more equal in size. Iowa distr ibution: Planted throughout the state and occasionally escaping.

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d e s c r i p t i o n s o f t r e e s p e c i e s 147

Bur Oak, Quercus macrocarpa Michx. Distinguishing ch a r acter istics: Leaves simple, alternate, variable in shape but commonly obovate, shallowly lobed above the middle with a pair of deeply cut sinuses near or below the middle, 6 to 10 inches long with petioles 1/3 to 1 inch long, dark green above, paler and finely hairy below. Buds clustered at twig tips, subglobose to ovoid, 1/8 to 1/4 inch long, densely covered with fine gray hairs. Acorns globe-shaped, 3/5 to 2 inches long, sessile or short-stalked; cup with a prominent fringe of soft bristles around its rim, covering 1/3 or more of the nut. Bark dark, thick, and deeply furrowed. Corky outgrowths often present on older twigs. Simila r tr ees: Leaves of white oak are hairless beneath with lobes of uniform size, and the leaves of swamp white oak lack deeply cut sinuses. Neither has bristles around the rims of its acorn-cups. Iowa distr ibution: Native throughout the state.

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White Oak, Quercus alba L. Distinguishing ch a r acter istics: Leaves simple, alternate, with 7 to 9 lobes, 5 to 9 inches long with petioles 1/2 to 1 inch long; lobes with rounded tips, variable in length from one leaf to the next but rather uniform in any given leaf; surfaces green and glabrous. Buds clustered at twig tips, subglobose, 1/8 to 3/16 inch long, glabrous or nearly so. Acorns oblong, 1/2 to 3/4 inch long, sessile or nearly so; cups bowl-shaped with thick, warty scales, covering the lower 1/4 of the nut. Bark light ashy-gray, separating into small, scaly plates; often furrowed with thick, blocky ridges on old trees. Simila r tr ees: Bur oak has hairy buds, fringed acorn-cups, and dark, furrowed bark; its leaves are not so uniformly lobed and are hairy beneath. Swamp white oak has long-stalked acorns and more shallowly lobed leaves that are hairy beneath. Leaves of English oak, which is sometimes planted in Iowa, have small, earlike lobes at the base of their blades. English oak also has stalked acorns. Iowa distr ibution: Native in eastern, central, and southern Iowa and locally in north central Iowa.

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Chinkapin Oak, Quercus muhlenbergii Engelm. Distinguishing ch a r acter istics: Leaves simple, alternate, oblonglanceolate to obovate, with 8 to 13 (usually 10 or more) pairs of veins and an equal number of large, usually sharp-pointed teeth; 4 to 7 inches long with petioles 3/4 to 1 1/2 inches long; glabrous and dark green or yellow-green above; paler and finely hairy below. Buds clustered at twig tips, ovoid, 1/8 to 1/4 inch long; bud scales glabrous with pale, often slightly hairy margins. Acorns ovoid, 1/2 to 3/4 inch long, sessile or nearly so; cups bowl-shaped with appressed scales, covering the lower 1/3 to 1/2 of the nut. Bark scaly, light ashy gray. Simila r tr ees: Leaves of swamp white oak have fewer veins and the teeth are blunt or rounded; swamp white oak also has larger, long-stalked acorns. Dwarf oak (Q. prinoides, see the discussion in part 2) is a shrubby species whose leaves have shorter petioles and only 5 to 8 pairs of veins. Iowa distr ibution: Native south and east of a line extending from the Loess Hills in Mills County northeastward to Winneshiek County.

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Swamp White Oak, Quercus bicolor Willd. Distinguishing ch a r acter istics: Leaves simple, alternate, obovate, with shallow lobes or blunt teeth and 6 to 8 pairs of veins, 5 to 7 inches long with petioles 1/2 to 3/4 inch long; upper surface dark green; lower surface paler and finely hairy. Buds clustered at twig tips, subglobose, 1/16 to 3/16 inch long, glabrous or nearly so. Acorns broad-ovoid, 3/4 to 1 1/4 inches long, paired at the ends of stalks 1 to 4 inches long; cups bowl-shaped, covering about 1/3 of the nut; cup scales slightly thickened, those around the rim of the cup pointing upward, forming a fringe. Bark of branches light ashy gray, separating into papery scales that peel off and reveal the greenish inner bark; trunk bark light gray to gray-brown, scaly, eventually furrowed with thick, blocky ridges. Simila r tr ees: Leaves of white oak are more deeply lobed and hairless beneath; leaves of chinkapin oak have more numerous veins and usually sharppointed teeth. Bur oak leaves have at least one pair of deeply cut sinuses near the middle. All three have sessile or short-stalked acorns. Iowa distr ibution: Native in eastern, central, and south central Iowa. Planted throughout most of state. Hybrids between swamp white and bur oak are also planted.

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Post Oak, Quercus stellata Wangenh. Distinguishing ch a r acter istics: Leaves simple, alternate, with 5 lobes, the upper 3 lobes much larger than the others and forming a cross, 4 to 6 inches long with petioles 1/2 to 1 inch long, dark green above, pale green to gray-green and finely hairy below. Buds clustered at twig tips, 1/8 to 1/4 inch long, sparsely hairy. Acorns ovoid, 1/2 to 2/3 inch long, sessile or nearly so; cups bowl-shaped with thin scales, covering 1/3 to 1/2 of the nut. Bark graybrown to light ashy gray, scaly, becoming furrowed on older trees. Simila r tr ees: Leaves of bur oak sometimes have 3 strongly developed upper lobes that suggest a cross, but the pattern is much more pronounced in the leaves of post oak. Bur oak also differs in having fringed acorn-cups and dark furrowed bark. Iowa distr ibution: Native in Lee, Henry, Van Buren, and Appanoose counties and possibly in other counties near the Missouri border.

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Red Oak, Quercus rubra L. (Q. borealis Michx.) Distinguishing ch a r acter istics: Leaves simple, alternate, with 7 to 11 lobes, 5 to 9 inches long with slender petioles 1 to 2 inches long; lobes bristletipped, usually no longer than the width of the central undivided portion of the blade (occasionally up to twice as long on leaves growing in full sun); sinuses U-shaped; upper surface glabrous and dull green; lower surface paler and glabrous except for small tufts of hairs in the axils of the large veins. Buds clustered at twig tips, ovoid, 1/8 to 3/8 (usually 3/16 to 1/4) inch long, rounded or slightly angled in cross section, glabrous or hairy just at the tip. Acorns ovoid, 1/2 to 1 inch long, sessile or nearly so; cups saucer-shaped to bowlshaped with red-brown, closely appressed scales, covering no more than the lower 1/3 of the nut. Bark at base of trunk light gray to nearly black; thick and deeply furrowed; appearing striped on upper trunk; with dark, flattened ridges alternating with smooth light gray areas. Inner bark light red. Simila r tr ees: The shallowly and evenly lobed leaves of red oak are quite different from the typical leaves of black, pin, and Hill’s oaks. Black oak, when its leaves are similar, can be distinguished by its large, strongly angled, densely hairy buds; yellow inner bark; and loose scales around the rim of its acorn-cups. Iowa distr ibution: Native as far west as the Missouri and Little Sioux rivers and the Spirit-Okoboji lakes chain. Often planted.

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Black Oak, Quercus velutina Lam. Distinguishing ch a r acter istics: Leaves simple, alternate, with 5 to 7 lobes, 5 to 9 inches long with moderately stout petioles 2 to 6 inches long; lobes bristle-tipped, usually with one pair much larger than the others and 2 to 6 times longer than the width of the central, undivided portion of the blade; sinuses broadly U-shaped or circular; upper surface dark green and glossy; lower surface paler and either glabrous or hairy. Buds clustered at twig tips, ovoid, 1/4 to 1/2 inch long, strongly angled in cross section, densely hairy. Acorns ovoid, 1/2 to 3/4 inch long, sessile or nearly so; cups bowl-shaped or cone-shaped with loose light brown, hairy scales forming a conspicuous fringe around the rim, covering 1/3 to 1/2 of the nut. Bark thick, dark, and furrowed on lower trunk, similar to red oak on upper trunk. Inner bark yellow. Simila r tr ees: The large, strongly angled, densely hairy buds and loosescaled acorn-cups easily distinguish black oak from red, pin, and Hill’s oak. Iowa distr ibution: Native in southern and eastern Iowa and local in the central and north central parts of the state. Many of the “black oaks” along the edge of the range are not typical of the species and may reflect hybridization with other oaks (see the discussion in part 2).

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Hill’s Oak or Northern Pin Oak, Quercus ellipsoidalis E. J. Hill

Distinguishing ch a r acter istics: Leaves simple, alternate, with 5 to 7 lobes, 3 to 5 inches long with slender petioles 1 to 2 inches long; lobes bristletipped, often much broader at the tip than the base, 2 to 6 times longer than the width of the central, undivided portion of the blade; sinuses U-shaped or circular; upper surface bright green, glabrous, and glossy; lower surface paler, glabrous except for tufts of hairs in the axils of the large veins. Buds clustered at twig tips, ovoid, 1/8 to 3/16 inch long, rounded to angled in cross section, usually hairy at the tips. Acorns broadly to narrowly football-shaped, 1/2 to 3/4 inch long, often striped with dark vertical lines, short-stalked to nearly sessile; cups cone-shaped with brown, hairy, tightly appressed scales, covering 1/3 to 1/2 of the nut. Bark similar to pin oak. Inner bark orangeish. Simila r tr ees: Black oak has larger, strongly angled, densely hairy buds and acorn-cups with loose scales. Pin oak has squat acorns with saucer-shaped cups, and its leaf lobes tend to be widest at the base. Red oak has shallowly lobed leaves and larger glabrous to nearly glabrous buds. Iowa distr ibution: Native in the northern half of the state west to the Little Sioux River, though not common in northwest Iowa.

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Pin Oak, Quercus palustris Muenchh. Distinguishing ch a r acter istics: Leaves simple, alternate, with 5 to 7 lobes, 3 to 6 inches long with slender petioles 1/2 to 2 inches long; lobes bristle-tipped, the larger ones 2 to 6 times longer than the width of the central, undivided portion of the blade, the lower pair curved downward and sometimes much smaller than the others; sinuses broadly U-shaped or circular; upper surface dark green, glabrous, and glossy; lower surface paler, glabrous except for tufts of hairs in the axils of the large veins. Buds clustered at twig tips, ovoid, 1/16 to 3/16 (usually about 1/8) inch long, slightly angled, glabrous (sometimes with fine hairs along the edges of the scales). Acorns hemisphereshaped, 3/8 to 1/2 inch long, often striped with dark vertical lines, sessile or nearly so; cups saucer-shaped with thin, appressed, red-brown scales, covering only the base of the nut. Bark on lower trunk gray-brown and shallowly furrowed, on upper trunk smooth and light gray, sometimes striped as in red oak. Simila r tr ees: Hill’s oak has football-shaped acorns seated in coneshaped cups that cover 1/3 to 1/2 of the nut, and its leaf lobes tend to be widest at the tip. Red oak has larger buds and acorns and shallowly lobed leaves with narrow sinuses. Black oak has larger, strongly angled, densely hairy buds, and its acorn-cups have loose scales around the rim. Iowa distr ibution: Native along the Mississippi River and its tributaries north to Jackson, Jones, Johnson, Keokuk, Appanoose, and Decatur counties. Commonly planted throughout the state.

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Blackjack Oak, Quercus marilandica Muenchh. Distinguishing ch a r acter istics: Leaves simple, alternate, obovate, shallowly 3-lobed, 5 to 7 inches long with stout petioles 3/8 to 3/4 inch long; upper surface dark green and glossy, lower surface paler and more or less hairy. Buds clustered at twig tips, ovoid, 1/4 to 3/8 inch long, strongly angled in cross section, densely covered with light brownish hairs. Acorns oblong to subglobose, about 3/4 inch long, sessile or nearly so; cups bowl-shaped with loose, hairy, light brown scales, covering about 1/2 of the nut. Bark dark brown to nearly black, divided into thick, blocky plates. Simila r tr ees: The 3-lobed leaves are distinctive. The only tree even remotely resembling it is its hybrid with black oak, which typically has 5-lobed leaves. Iowa distr ibution: The species (or its hybrid with black oak, see part 2) is native locally from Lee County north to Louisa County and west to Marion, Union, and Decatur counties.

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d e s c r i p t i o n s o f t r e e s p e c i e s 167

Ginkgo, Ginkgo biloba L. Distinguishing ch a r acter istics: Leaves simple, alternate on twigs but clustered at the ends of spur shoots on branchlets, fan-shaped, lobed or not, entire. Winter twigs moderate in diameter, with shreddy outer bark; leaf scars small, half-round, each with 2 bundle scars. Buds subglobose with brown overlapping scales, about 3/16 inch long; terminal bud present. Flowers absent (see discussion of reproductive structures in part 2). Seed plumlike, stalked, about 1 inch long, with fetid yellow flesh and nutlike center. Bark gray-brown, with long scaly ridges and shallow furrows. Simila r tr ees: No other tree has leaves of this shape. In winter, larches have small cones; all other trees with spur shoots on their twigs have 3 or more bundle scars. Iowa distr ibution: Planted throughout the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 169

Tulip Tree, Liriodendron tulipifera L. Distinguishing ch a r acter istics: Leaves simple, alternate, 4-lobed with shallowly notched apices, 4 to 6 inches long, entire. Winter twigs moderate in diameter, dark red-brown, aromatic when cut; stipule scars forming a ring around the twig at each node; leaf scars conspicuous, round, with several bundle scars. Buds duckbill-shaped with 2 green or dark red scales that meet along the edges without overlapping, the terminal about 1/2 inch long and the laterals much smaller. Flowers large, perfect, tuliplike, yellow-green marked with orange on the inside, solitary at the twig tips, blooming in early summer. Fruit a conelike aggregate of samaras, persisting on the twigs in winter. Bark light gray, shallowly furrowed. Simila r tr ees: No other tree has leaves of this shape. In winter, the duckbill-shaped, 2-scaled buds are distinctive. Iowa distr ibution: Planted where hardy in the eastern, southern, and central parts of the state.

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Sweetgum, Liquidambar styraciflua L. Distinguishing ch a r acter istics: Leaves simple, alternate, 3 1/2 to 7 inches long, star-shaped with 5 to 7 palmate lobes, the margins of the lobes toothed. Winter twigs moderate, green or brown, often developing corky outgrowths their second year, sometimes developing spur shoots as well; leaf scars half-round to somewhat crescent-shaped, each with 3 bundle scars. Buds ovoid, brown, the terminal 1/4 to 1/2 inch long with 6 to 8 overlapping scales, the laterals somewhat smaller. Flowers small, green, monoecious, the staminate in racemes and the pistillate in ball-shaped heads, appearing with the leaves in spring. Fruit ball-shaped, woody, prickly, brown, 1 to 1 1/2 inches in diameter, composed of many small capsules, persisting on the twigs in winter. Bark gray-brown, furrowed. Simila r tr ees: Some maples have similar leaves, but maple leaves are opposite. In winter, its peculiar fruits make this species easy to recognize. Iowa distr ibution: Planted where hardy in the southern part of the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 173

Sycamore, Platanus occidentalis L. Distinguishing ch a r acter istics: Leaves simple, alternate, 4 to 7 inches long, palmately 3- to 5-lobed with the margins of the lobes coarsely toothed. Winter twigs moderate in diameter, glabrous, orange-brown to light brown; stipule scars forming a ring around the twig at each node; leaf scars ring-shaped, completely encircling the buds, each with 5 to 9 bundle scars. Buds cone-shaped, 1/4 to 3/8 inch long, hidden within the base of the petiole, each covered with a single glabrous brown scale, the terminal bud absent. Flowers very tiny, monoecious, crowded in small, ball-shaped heads that appear when the leaves are unfolding in late spring. Fruit ball-shaped, about 1 inch in diameter, on a slender stalk 3 to 6 inches long, composed of numerous tiny achenes bearing tufts of brown hairs. Bark of branches and upper trunk either smooth and chalk white or mottled with thin, irregularly shaped patches of white and tan; on lower trunks composed of small light gray or reddish brown plates. Simila r tr ees: Maple leaves are similar in shape but arranged oppositely on the twigs. In winter, the sycamore is unique in having both twig-encircling stipule scars and bud-encircling leaf scars. Iowa distr ibution: Native or naturalized across most of the southern one-half to two-thirds of the state. Cultivated throughout.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 175

White Mulberry, Morus alba L. Distinguishing ch a r acter istics: Leaves simple, alternate, either lobed or unlobed (both types usually present on same tree), ovate-oval, 2 1/2 to 4 (rarely up to 7) inches long with petioles 3/8 to 1 inch long; sap milky; margins with coarse and usually blunt teeth; base heart-shaped or truncate; apex blunt or short-pointed; upper surface glabrous and glossy; lower surface glabrous or with hairs restricted to the larger veins and vein axils. Winter twigs very slender, glabrous, gray-brown; leaf scars small, half-round to nearly round, concave, with 6 or more bundle scars. Buds globose or triangular, about 1/8 inch long, closely appressed to the twig, the terminal absent; scales 3 to 6, brown, glabrous. Flowers monoecious or dioecious, in catkins, appearing with the leaves in late spring. Fruit blackberrylike, 1/8 to 1 inch long, red or purple (rarely white) when ripe. Bark smooth and light orange-brown on young trees and branches of large trees, brown and furrowed on trunks of mature trees. Simila r tr ees: Red mulberry has larger leaves with hairy undersurfaces and long-pointed tips. In winter, red mulberry has ovoid buds that angle away from the twigs; all other trees with similar twigs have only 3 bundle scars. Iowa distr ibution: Naturalized throughout the state.

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Red Mulberry, Morus rubra L. Distinguishing ch a r acter istics: Leaves simple, alternate, broadly ovate or oval, often with 2 to 5 lobes on younger shoots, 3 to 9 inches long with petioles 3/4 to 1 1/4 inches long; sap milky; margins toothed; base more or less heart-shaped; apex acuminate; upper surface either glabrous or rough hairy; lower surface finely hairy along veins. Winter twigs slender, reddish brown, glabrous; leaf scars small, nearly round, concave, with 6 or more bundle scars. Buds ovoid, 1/8 to 1/4 inch long, the terminal absent; scales 3 to 6, greenish brown with dark-colored margins. Flowers monoecious or dioecious, in catkins, appearing with leaves in late spring. Fruit blackberrylike, oblong, 1 to 1 1/4 inches long, dark purple when ripe. Bark dark brown with a reddish tinge, dividing into shallow furrows and scaly ridges. Simila r tr ees: White mulberry has smaller leaves that are much less hairy beneath. Unlobed leaves of red mulberry are sometimes confused with those of American basswood, but the latter are more rounded in shape and essentially glabrous beneath. In winter, white mulberry has appressed buds that are typically as wide as long; all other trees with similar twigs have only 3 bundle scars. Iowa distr ibution: Native across the southern half of the state, north along the Mississippi River to the Minnesota border and the Des Moines River to Webster County, also reported in Winneshiek and Delaware counties. Hybrids between this and white mulberry have been reported where the two species grow in the same locality.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 179

Downy Hawthorn or Red Haw, Crataegus mollis (T. & G.) Scheele

Distinguishing ch a r acter istics: Leaves simple, alternate, broadly ovate, shallowly lobed, 2 1/2 to 4 inches long, toothed, often hairy beneath; petioles stout, usually hairy, 3/4 to 2 inches long. Winter twigs slender to moderate in diameter, usually armed with sharp, slender, smooth, unbranched thorns 1 to 2 1/2 inches long; leaf scars small, half-round to crescent-shaped, with 3 bundle scars. Buds globose to subglobose with about 6 glabrous, fleshy, and usually reddish scales; lateral buds often nearly equal to the terminal in size. Flowers perfect, regular, in showy corymblike clusters, appearing with the leaves in spring; petals white, roundish. Fruit apple-like, 1/2 to 3/4 inch in diameter, bright red when ripe, with 4 or 5 seeds and thick, juicy flesh; deciduous in autumn. Simila r tr ees: Wild crabapple has much larger greenish fruits, and its “thorns” have leaves growing on them. (Hawthorns have no leaves on the thorns.) Other, less common hawthorns have leaves either unlobed or not so obviously lobed and differ subtly in flower and fruit characteristics; see the keys in this book for more information. In winter, the combination of smooth thorns and red buds is unique to hawthorns. The various species of hawthorns are not easily distinguished in winter. Iowa distr ibution: Native throughout the state, our most common and widespread hawthorn.

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d e s c r i p t i o n s o f t r e e s p e c i e s 181

Prairie Crabapple,

Malus ioensis (Wood) Brit. [Pyrus ioensis (Wood) Carruth.] Distinguishing ch a r acter istics: Leaves simple, alternate, oblongovate, shallowly lobed, 2 1/4 to 4 inches long, toothed, persistently hairy beneath and on the petioles. Winter twigs moderate in diameter, hairy, thorny (with leaf scars on the thorns); leaf scars linear or crescent-shaped, small, with 3 bundle scars. Buds subglobose to ovoid, small, few-scaled, hairy. Flowers showy, perfect, regular, pink or white, appearing with the leaves in spring. Fruit a green pome 3/4 to 1 inch in diameter. Simila r tr ees: Our only native crabapple. Downy hawthorn is somewhat similar but has much smaller red fruits, no leaves or leaf scars on its thorns, glabrous twigs, and glabrous red buds. Iowa distr ibution: Native in all but the extreme northwest corner of the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 183

White Poplar, Populus alba L. Distinguishing ch a r acter istics: Leaves simple, alternate, oval to nearly round in outline, with 3 to 5 lobes or with a few irregularly sized teeth, 2 to 5 inches long; lower surface and petiole with a white feltlike coating. Winter twigs slender to moderate in diameter, olive-green to gray, densely covered with a white feltlike material; leaf scars half-round or crescent-shaped, small, with 3 bundle scars. Buds ovoid, the terminal 1/8 to 1/4 inch long and the laterals often of two sizes, divergent from the twig, the lowermost scale of each centered directly above the leaf scar; bud scales brown, partially to completely covered with matted white hairs. Flowers dioecious, in catkins, appearing before the leaves in spring. Fruit a flask-shaped capsule about 1/8 inch long, opening in late spring and releasing the tiny cottony, windblown seeds. Bark on upper trunk and larger branches thin, smooth, white, with numerous black warty outgrowths, black and furrowed at base. Simila r tr ees: Mature leaves of bigtooth aspen are glabrous beneath. In winter, no other white-barked tree has a white feltlike coating on its twigs. Iowa distr ibution: Planted throughout the state, frequently persisting and spreading on abandoned land because of root suckering.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 185

Eastern Cottonwood, Populus deltoides Bartr. Distinguishing ch a r acter istics: Leaves simple, alternate, broadly triangular in shape, 3 to 6 inches long, glabrous, toothed; petiole flattened, 1 1/2 to 3 inches long, with 2 or 3 tiny glands at its junction with the blade. Winter twigs moderate in diameter, glabrous, gray or gray-green; pith star-shaped in cross section; leaf scars variably shaped and sized, with 3 bundle scars. Buds ovoid, the terminal bud 3/8 to 3/4 inch long and the lateral buds often of two sizes, the lowermost scale of each centered directly over the leaf scar; bud scales yellow or brown, glabrous, slightly sticky. Flowers dioecious, in catkins, appearing before the leaves in spring. Fruit a flask-shaped capsule about 1/3 inch long, opening in early summer and releasing the tiny cottony, windblown seeds. Bark thin, smooth, and light gray-green on young trees, eventually thick and deeply furrowed with long light gray ridges. Simila r tr ees: The triangular leaves are distinctive. In winter, cottonwood and aspens differ from other trees in having the lowermost scale of their lateral buds centered over the leaf scar. Aspens differ from cottonwood in the color of their bark and twigs. Iowa distr ibution: Native throughout the state. Occasionally planted.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 187

Quaking Aspen, Populus tremuloides Michx. Distinguishing ch a r acter istics: Leaves simple, alternate, nearly round, 1 1/2 to 3 inches in diameter, glabrous, with 20 to 40 small teeth on each side; petiole flattened, 1 1/2 to 3 inches long. Winter twigs slender, glabrous, dark brown; leaf scars half-round or crescent-shaped, small, with 3 bundle scars. Buds ovoid, the terminal 1/4 to 3/8 inch long and the laterals often of two sizes, closely appressed to the twig, each with its lowermost scale centered directly over the leaf scar; bud scales shiny dark brown, glabrous, slightly sticky. Flowers dioecious, in catkins, appearing before the leaves in early spring. Fruit a flask-shaped capsule about 1/4 inch long, opening in late spring and releasing the tiny cottony, windblown seeds. Bark smooth, thin, white or greenish white, with black warty thickenings, becoming dark and furrowed at the base of the tree. Simila r tr ees: Leaves of bigtooth aspen have fewer and larger teeth, and those of paper birch are ovate with short, rounded petioles. In winter, bigtooth aspen and white poplar have dull, hairy buds that angle away from the twigs. Birches have catkins and lack terminal buds. Iowa distr ibution: Native. Common in eastern Iowa, rare and local elsewhere.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 189

Bigtooth Aspen, Populus grandidentata Michx. Distinguishing ch a r acter istics: Leaves simple, alternate, broadly ovate, 2 to 5 inches long, glabrous when mature, with 5 to 15 large, blunt teeth on each side; petiole flattened, 1 1/2 to 2 1/2 inches long. Winter twigs moderate in diameter, brown, either glabrous or finely gray-hairy; leaf scars similar to quaking aspen. Buds ovoid, the terminal 3/16 to 1/4 inch long and the laterals often of two sizes, slightly divergent from the twig, the lowermost scale of each centered directly over the leaf scar; bud scales brown, partially covered with fine gray hairs. Flowers dioecious, in catkins, appearing before the leaves in early spring. Fruit a flask-shaped capsule 1/8 to 3/16 inch long, opening in late spring and releasing the tiny cottony, windblown seeds. Bark thin, smooth, dull yellow-green to nearly white on upper trunk; dark brown with broad, flattened ridges and narrow furrows on lower trunk. Simila r tr ees: Quaking aspen has smaller, more numerous leaf teeth and glossy dark brown buds. Leaf undersurfaces, petioles, and twigs of white poplar are covered with matted white hairs. Iowa distr ibution: Native as far west as the Des Moines River valley (west fork), also reported in woods along the Little Sioux River in Clay County.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 191

Black Willow, Salix nigra Marsh. Distinguishing ch a r acter istics: Leaves simple, alternate, nar­rowly lanceolate, gradually tapered to slender tips, 3 to 6 inches long with petioles 1/8 to 1/4 inch long, finely and closely toothed (teeth usually 18 to 25 per inch of margin at midleaf); lower surface light green and glabrous (sometimes minutely hairy along the midvein). Winter twigs very slender, glabrous, gray-brown to brown, very brittle at base; leaf scars small, linear or crescent-shaped with 3 bundle scars. Buds ovoid, one-scaled, 1/16 to 3/16 inch long, the terminal absent; bud scale glabrous, its edges freely overlapping on the back (twig) side of the bud, often with a distinct basal band different in color from its brown upper portion. Flowers dioecious, in catkins, appearing in spring at the ends of expanding leafy shoots. Fruit a flask-shaped capsule about 1/8 inch long, opening in summer and releasing the tiny cottony, windblown seeds. Bark dark brown to nearly black, deeply furrowed with thick, scaly ridges. Simila r tr ees: Sandbar willow, the only other tree having very narrow, short-petioled leaves with green undersurfaces, is a much smaller, colonial tree with widely spaced leaf teeth. In winter, peachleaf willow is very similar, though usually distinguishable by the color of the twigs and buds and shape of the leaf scars. Other large willows have buds with caplike scales showing no visible edges. Iowa distr ibution: Native as far west as the Missouri River and the natural lakes district of northwestern Iowa.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 193

Peachleaf  Willow, Salix amygdaloides Anderss. Distinguishing ch a r acter istics: Leaves simple, alternate, lanceolate to ovate-lanceolate; gradually or abruptly tapered to long, slender, often tail-like tips; 2 to 5 inches long with slender, frequently twisted petioles 1/4 to 3/4 inch long; margins finely and closely toothed; lower surface glabrous and pale bluish green. Winter twigs very slender, glabrous, usually light yellow or yellowish gray; leaf scars small, U-shaped, with 3 bundle scars. Buds similar to black willow except upper portion of scale often yellow or black. Flowers and fruits similar to black willow. Bark brown, deeply furrowed with flat, scaly ridges. Simila r tr ees: Leaves of black and sandbar willow are narrower and green beneath with shorter petioles. The only other willows that regularly reach tree size are Eurasian species with thicker, glossy leaves. In winter, see black willow. Iowa distr ibution: Native throughout the state.

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d e s c r i p t i o n s o f t r e e s p e c i e s 195

Sandbar Willow,

Salix interior Rowlee (S. exigua Nutt. ssp. interior [Rowlee] Cronq.) Distinguishing ch a r acter istics: Small tree or shrub, often forming colonies. Leaves simple, alternate, linear to linear-lanceolate, tapered to pointed tips, 2 to 6 inches long with petioles up to 1/8 inch long; margins distantly toothed (teeth 3 to 11 per inch of margin); lower surface green and either glabrous or sparsely hairy. Winter twigs very slender, glabrous or finely hairy, usually reddish brown in color; leaf scars small, linear, with 3 bundle scars. Buds ovoid, 1/16 to 3/16 inch long, often paired above some of the leaf scars, terminal absent; bud scale glabrous, yellow or brown, caplike with no free edges. Flowers dioecious, in catkins at the ends of long, leafy shoots. Fruit a flask-shaped capsule about 1/3 inch long, opening in summer and releasing the tiny cottony, windblown seeds. Bark gray to brown, smooth, becoming scaly at the base of larger stems. Simila r tr ees: Differs from black and peachleaf willows by its small size, colonial habit, narrower leaves, and widely spaced leaf teeth. In winter, bud scales of black and peachleaf willows have freely overlapping edges. Iowa distr ibution: Native throughout the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 197

River Birch, Betula nigra L. Distinguishing ch a r acter istics: Leaves simple, alternate on twigs, in pairs on spur shoots, ovate with a wedge-shaped base, 1 1/2 to 3 1/4 inches long with petioles about 1/2 inch long; margins toothed; veins running directly into the teeth. Winter twigs slender, glabrous, red-brown to orangebrown, dotted with conspicuous white lenticels; catkins usually present; leaf scars small, half-round to crescent-shaped, with 3 bundle scars. Buds ovoid, the terminal present on spur shoots but absent from twigs, the laterals about 1/4 inch long, with 3 or 4 brown scales that may be either hairy or glabrous. Flowers monoecious, in catkins, appearing with or shortly before the leaves in spring. Fruit a tiny winged nutlet borne in a conelike catkin 1 to 1 1/2 inches long. Bark on young trees flaking into thin, papery pieces that are at first orange and white and later orange-brown; bark of mature trees scaly and dark red-brown to nearly black. Simila r tr ees: Paper birch and introduced ornamental birches have chalky white bark with no trace of orange. The bark of large river birches is very similar to that of black cherry, which has oblong-lanceolate leaves, no winter catkins, and red buds with more than 4 scales. Iowa distr ibution: Native through most of the eastern third of Iowa and in scattered localities in the southern part of the state west to Adams County. Cultivated throughout the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 199

Paper Birch, Betula papyrifera Marsh. Distinguishing ch a r acter istics: Leaves simple, alternate on twigs, paired on spur shoots, ovate to oval, 2 to 3 (rarely 5) inches long with petioles 1/2 to 3/4 inch long; margins toothed; bases rounded or truncate; veins running directly into the teeth. Winter twigs slender, glabrous, red-brown, dotted with conspicuous white lenticels; catkins usually present; leaf scars small, halfround to crescent-shaped, with 3 bundle scars. Buds ovoid, the terminal present on spur shoots but absent from twigs, the laterals about 1/4 inch long with 3 or 4 brown glabrous scales. Flowers similar to river birch. Fruit a tiny winged nutlet borne in a conelike catkin 1 to 1 1/2 inches long. Bark smooth, white, peeling into papery strips. Simila r tr ees: Leaves of other white-barked birches are triangular to diamond-shaped in outline. (For more information about these other species, see part 2.) Quaking aspen, which also has white bark, has round leaves with long, flattened petioles and no catkins in winter. Iowa distr ibution: Native from Allamakee County west to Mitchell County and south to Linn, Delaware, and Jackson counties; also along the Iowa River in Hardin County. Cultivated throughout the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 201

Yellow Birch, Betula alleghaniensis Britton (B. lutea Michx.) Distinguishing ch a r acter istics: Leaves simple, alternate on twigs, paired on spur shoots, ovate to oblong-ovate, 3 to 4 1/2 inches long with petioles 3/4 to 1 inch long; margins toothed; bases rounded and often unequal; veins running directly into the teeth. Winter twigs slender, glabrous, brown, dotted with conspicuous white lenticels, releasing a distinct wintergreen odor when bruised; catkins usually present; leaf scars small, half-round to crescentshaped, with 3 bundle scars. Buds ovoid, the terminal present on spur shoots but absent from twigs, the laterals about 1/4 inch long with 3 or 4 brown scales hairy along the edges. Flowers similar to river birch. Fruit a tiny winged nutlet borne in a conelike catkin 1 to 1 1/2 inches long. Bark light gray or yellow-gold, smooth when young, then separating into scales or thin, rolled strips. Simila r tr ees: Small trees can be distinguished from ironwood, elms, serviceberries, and other trees with similar leaves by the wintergreen odor of bruised twigs and the presence of spur shoots on the branchlets. The thin, scaly bark of mature trees is distinctive. Iowa distr ibution: Native in extreme northeastern Iowa west to Mitchell County and south to Dubuque County, also native along the Iowa River in Hardin County.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 203

American Hazel, Corylus americana Walt. Distinguishing ch a r acter istics: Shrub. Leaves simple, alternate, broadly ovate, 2 to 5 inches long, coarsely toothed, with the veins running to the tips of the teeth; petioles and young twigs covered with stiff, erect, glandtipped hairs. Winter twigs slender, brown, with ashy gray exposed catkins; leaf scars small, half-round, with 3 bundle scars. Buds globose to subglobose, about 1/8 inch long, with 4 to 6 brown scales. Flowers monoecious, in catkins; pistillate catkins short and concealed by the bud scales except for their protruding red stigmas; staminate catkins long and exposed, blooming before the leaves appear in early spring. Fruit an edible nut about 1/2 inch in diameter, enclosed by a pair of leathery leaflike bracts. Simila r tr ees: Common and possibly mistaken for a tree sapling in the woods, but differing from native trees in the broader, more unevenly toothed leaves and glandular petioles, ashy gray winter catkins, and distinctive fruits. Beaked hazel, native in northeastern Iowa, differs in having the fruit bracts elongated into a tubelike beak. Iowa distr ibution: Native throughout the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 205

Ironwood or Hop Hornbeam, Ostrya virginiana (Mill.) K. Koch

Distinguishing ch a r acter istics: Leaves simple, alternate, oblongovate, 3 to 5 inches long with petioles about 1/4 inch long, toothed; some of the veins forking, others running unforked into the teeth. Winter twigs very slender, brown, often hairy; catkins often present; leaf scars very small, half-round, with 3 bundle scars. Buds ovoid, 1/8 to 1/4 inch long, the terminal absent; bud scales green and brown, usually 6 to 9 in number, spirally arranged, glabrous or hairy, their surfaces creased with fine vertical lines (seen with magnifying glass). Flowers monoecious, in catkins, appearing with the leaves in spring. Fruit a nutlet about 1/3 inch long enclosed in a small papery sac; sacs overlapping one another in hoplike clusters 1 1/2 to 2 inches long. Bark gray or brown, unbroken on young trees but eventually separating into vertical rows of small, rectangular plates that are typically appressed to the trunk but sometimes loose and shaggy. Simila r tr ees: Other trees with similar leaves have leaf veins all running unforked into the teeth (elms, American hornbeam, yellow birch) or ending before reaching the margin (cherries, serviceberries). The hoplike fruit clusters are also distinctive. In winter, bud scales of other trees are not creased with vertical lines. Iowa distr ibution: Native throughout the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 207

American Hornbeam, Carpinus caroliniana Walt. Distinguishing ch a r acter istics: Leaves simple, alternate, ovate to oval, 2 to 4 inches long with petioles about 1/3 inch long, toothed; veins running directly into the teeth. Winter twigs very slender, red-brown, glabrous; leaf scars very small, half-round, with 3 bundle scars. Buds ovoid, about 1/8 inch long, the terminal absent; bud scales about 12, arranged in four vertical rows, brown or red with white margins, glabrous or nearly so. Flowers monoecious, in catkins, appearing with the leaves. Fruit a nutlet about 1/3 inch long attached to the base of a leafy, 3-lobed bract 1 to 1 1/2 inches long; bracts overlapping one another in a dense cluster 2 to 4 inches long. Bark light gray, very smooth. Trunks with a distinctive twisted or muscled appearance, often growing in clumps. Simila r tr ees: Other trees (for example, serviceberries) have smooth bark, but their trunks lack the muscled appearance of hornbeam. Iowa distr ibution: Native through most of the eastern third of Iowa, also in the Iowa and Des Moines River valleys in the central part of the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 209

American Elm, Ulmus americana L. Distinguishing ch a r acter istics: Leaves simple, alternate, elliptic, 4 to 6 inches long with petioles about 1/4 inch long, doubly toothed; base unequal, surfaces glabrous or hairy; veins running directly into the teeth. Winter twigs slender to moderate in diameter, usually glabrous and reddish brown, left scars similar to American elm. Buds 1/8 to 1/4 inch long, the flower buds larger and plumper than the ovoid leaf buds; scales 6 to 10, red-brown with dark margins, glabrous or nearly so, arranged in two vertical rows; the terminal bud absent. Flowers green, tinged with red, very small, perfect, without petals, on slender stalks up to 1 inch long, appearing in small, umbellike clusters before the leaves unfold in early spring. Fruit a broadly oval, 1-seeded samara about 1/2 inch long; wing glabrous with a hairy margin, broken at its apex by a deep notch extending nearly to the top of the seed cavity. Bark gray to gray-brown, divided into long, flat, scaly ridges separated by shallow to rather deep furrows; bark with alternating white and red-brown layers when viewed in cross section. Simila r tr ees: Slippery elm has ashy gray twigs and dark purple buds with copper-colored hairs. Ironwood, which resembles a small elm, has leaves with equal or nearly equal bases. Its green and brown bud scales are spirally arranged and marked with fine parallel lines. Ironwood also has winter catkins and a very distinctive fruit. Iowa distr ibution: Native throughout the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 211

Slippery Elm, Ulmus rubra Muhl. Distinguishing ch a r acter istics: Leaves simple, alternate, elliptic, 4 to 7 inches long with petioles about 1/3 inch long, doubly toothed; base unequal; upper surface dark green and rough-hairy, lower surface paler and hairy; veins running directly into the teeth. Winter twigs slender to moderate in diameter, ashy gray and often rough; bundle scars usually 3 (often compound into 4, 5, or 6), depressed within the surface of a pale brown corky layer covering each of the small, half-round leaf scars. Buds 1/8 to 1/4 inch long, ovoid (leaf buds) to nearly globose (flower buds), the terminal absent; bud scales 6 to 10, dark purple, more or less covered with copper-colored hairs, overlapping in two vertical rows. Flowers green, very small, perfect, without petals, on stalks about 1/16 inch long, appearing in umbellike clusters before the leaves unfold in early spring. Fruit a 1-seeded, nearly round samara about 1/2 inch in diameter; wing glabrous, its apex shallowly notched; seed cavity distinct. Bark similar to American elm but uniformly red-brown in cross section. Simila r tr ees: Siberian elm has smaller leaves and buds with white hairs along the margins of the bud scales. Buds of American elm are red-brown with dark margins and lack copper-colored hairs. Iowa distr ibution: Native throughout the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 213

Rock Elm, Ulmus thomasii Sarg. Distinguishing ch a r acter istics: Leaves simple, alternate, elliptic to obovate, 2 1/2 to 5 inches long with petioles about 1/4 inch long, doubly toothed; base equal or slightly unequal; upper surface glabrous; lower surface slightly hairy; veins running directly into the teeth. Winter twigs slender to moderate in diameter, glabrous to slightly hairy, light reddish brown; branchlets gray-brown with thick, corky outgrowths. Buds ovoid, 1/8 to 1/4 inch long, gradually tapered to sharp-pointed tips, the terminal absent; bud scales 6 to 10, brown with dark margins, more or less hairy, arranged in two vertical rows. Flowers very small, perfect, without petals, on slender stalks up to 1/2 inch long, appearing in small racemes before the leaves in early spring. Fruit an obovate, 1-seeded samara about 1/2 inch long; wing hairy, shallowly notched at apex; seed cavity indistinct. Bark similar to American elm. Simila r tr ees: American and slippery elms have strongly unequal leaf bases, and their branchlets lack corky outgrowths. Iowa distr ibution: Native throughout most of northeastern and north central Iowa, also in scattered localities in the southern part of the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 215

Siberian Elm, Ulmus pumila L. Distinguishing ch a r acter istics: Leaves simple, alternate, elliptic to elliptic-lanceolate, 1 to 3 inches long with petioles 1/16 to 1/8 inch long, toothed; base slightly unequal; upper surface glabrous; lower surface glabrous or nearly so; veins running directly into the teeth. Winter twigs very slender, light gray or gray-green, glabrous or nearly so; leaf scars very small, otherwise similar to slippery elm. Buds ovoid or globose, 1/16 to 3/16 inch long, the terminal absent; scales 6 to 10, dark purple-brown, shiny, glabrous except for white hairs along their margins. Flowers green, very small, perfect, without petals, on stalks about 1/16 inch long, appearing in crowded, umbellike clusters before the leaves unfold in spring. Fruit a 1-seeded, nearly round samara about 1/2 inch in diameter; wing glabrous, shallowly notched, seed cavity distinct. Bark gray-brown, shallowly furrowed with long scaly ridges, uniformly red-brown in cross section. Simila r tr ees: Other elms have much larger, doubly toothed leaves and larger buds. Iowa distr ibution: Cultivated throughout the state, often escaping to waste places. Hybrids between this species and the slippery elm are sometimes encountered.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 217

Hackberry, Celtis occidentalis L. Distinguishing ch a r acter istics: Leaves simple, alternate, ovate, 2 1/2 to 4 inches long with petioles 1/3 to 1/2 inch long; margins toothed (sometimes entire at base); veins forming a network near the margin, the largest three meeting in a single point at the base. Winter twigs very slender, light brown to gray-brown, usually glabrous; pith chambered at the nodes; leaf scars very small, half-round, with 3 (sometimes 1) bundle scars. Buds about 1/8 inch long, ovoid to triangular, closely appressed to the twig, the terminal absent; visible bud scales usually 3 or 4, light brown, finely and rather inconspicuously hairy. Flowers very small, greenish yellow, either perfect or imperfect, apetalous, on slender stalks, solitary or in small clusters from the axils of the newly unfolded leaves in spring. Fruit a dark purple drupe about 1/3 inch in diameter. Bark light to dark gray with distinctive warty outgrowths. Simila r tr ees: No other tree has ovate leaves with three veins meeting at the base. The hackberry’s warty bark, which is present even on small trees, is also unique. Iowa distr ibution: Native throughout the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 219

Flowering Crabapples, Malus Mill. (Pyrus L.) Distinguishing ch a r acter istics: Leaves simple, alternate, elliptic to oval in shape (lobed in some varieties), toothed; veins usually ending or forming a network near the margin. Winter twigs moderate in diameter, usually with spur shoots; leaf scars linear or crescent-shaped, small, with 3 bundle scars. Buds small, subglobose to ovoid, with several scales that are hairy at least along the edges. Flowers showy, perfect, regular, in corymb- or umbellike clusters at the ends of the spur shoots, appearing shortly before, with, or shortly after the leaves in spring; petals 5 to many, white, pink, or reddish, obovate to round; styles joined at base. Fruit a pome, variously sized and colored, but commonly small and berrylike, bright red or yellow, often persisting in winter. Bark smooth or scaly, gray to reddish brown in color. Simila r tr ees: Red- and pink-flowered crabs are not likely to be mistaken for other trees, as no other tree has flowers of their shape and color. (Redbud has much smaller, irregular flowers.) White-flowered crabs can be distinguished from serviceberries by their broad petals and later blooming time and from Callery pear by their united styles and usually later blooming time. At other seasons, crabs can be distinguished from other small trees by buds and fruits. Iowa distr ibution: Commonly planted throughout the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 221

Callery Pear, Pyrus calleryana Dcne. Distinguishing ch a r acter istics: Leaves simple, alternate, ovate to nearly round, 1 1/2 to 3 inches long, glabrous and often glossy, toothed. Winter twigs moderate in diameter, brown; leaf scars small with 3 bundle scars. Buds with several scales, often rather large, hairy. Flowers showy, perfect, regular, in corymblike clusters just before the leaves appear; petals 5, white, roundish; styles not joined at base. Fruit a pome about 3/8 inch in diameter, brown with pale dots. Bark gray to brown, becoming shallowly furrowed with age. Simila r tr ees: Flowering crabapples have elliptic to oval leaves, smaller buds, flowers with the styles joined at the base, and more conspicuous red or yellow fruits. Iowa distr ibution: Planted throughout the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 223

Cockspur Hawthorn, Crataegus crus-galli L. Distinguishing ch a r acter istics: Leaves simple, alternate, obovate to oblanceolate, with wedge-shaped bases, 1 to 4 inches long, leathery, glabrous, and glossy; petioles stout, 1/4 to 3/8 inch long. Winter twigs slender to moderate in diameter, armed with sharp unbranched thorns 2 to 7 inches long (absent in variety inermis); leaf scars small, half-round to crescent-shaped, with 3 bundle scars. Buds globose to subglobose with about 6 glabrous, fleshy, and usually reddish scales; lateral buds often nearly equal to the terminal in size. Flowers perfect, regular, in showy corymblike clusters, appearing with the leaves in spring; petals 5, white, roundish. Fruit a pome, red when ripe, about 3/8 inch in diameter, with 1 or 2 seeds and thin, dry flesh, persisting in winter. Simila r tr ees: The unlobed, glossy leaves and long thorns easily distinguish this species from other Iowa trees. Iowa distr ibution: Native in the southern half of the state, sometimes planted.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 225

Downy Serviceberry, Amelanchier arborea (Michx.) Fern. Distinguishing ch a r acter istics: Leaves simple, alternate, ovate to slightly obovate, 2 to 4 inches long with petioles 1/2 to 1 1/2 inches long, toothed, slightly heart-shaped at base; surfaces densely white-hairy when unfolding in spring but eventually glabrous or only slightly hairy beneath; veins branching freely and forming a network near the margin. Winter twigs slender, glabrous, red-brown to gray; leaf scars linear or crescent-shaped, very small, with 3 bundle scars. Buds elongate, the terminal 1/4 to 1/2 inch long and the laterals often nearly equal in size; scales commonly 4 to 6 in number, either red or yellow-green tinged with red. Flowers perfect, regular, in showy racemes, appearing when the leaves are beginning to expand in early spring; petals 5, white, linear to narrowly oblong. Fruit a reddish purple pome about 1/4 inch in diameter, ripening in early to midsummer. Bark light gray and very smooth, becoming darker and shallowly furrowed at the base of older stems. Simila r tr ees: Easily distinguished from other small flowering trees by its narrow petals and in summer by its small, early-ripening fruits and elongated buds. In winter, hornbeam has much shorter buds and muscled trunks. Iowa distr ibution: Native throughout eastern, southern, and central Iowa, also occurring though uncommon in the natural lakes area and the Des Moines River valley in northwestern Iowa.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 227

Black Cherry, Prunus serotina Ehrh. Distinguishing ch a r acter istics: Leaves simple, alternate, oblonglanceolate, 2 to 6 inches long with petioles 1/2 to 3/4 inch long; margins finely toothed, the tips of the teeth curving inward; 1 or 2 glands normally present on the upper portion of the petiole near the base of the blade. Winter twigs slender, red-brown, glabrous; leaf scars small, half-round, with 3 bundle scars. Buds ovoid, 1/8 to 1/4 inch long (occasionally larger), with about 6 glabrous, dark red-brown scales; the terminal bud equal to or only slightly larger than the laterals. Flowers perfect, regular, in showy racemes, appearing shortly after the leaves in mid to late spring; petals 5, white, broadly obovate. Fruit a drupe about 1/3 inch in diameter, purple-black when ripe, with a persistent calyx. Bark smooth with prominent lenticels, eventually separating into thin, light gray to black scales with upturned edges. Simila r tr ees: Chokecherry and wild plum are much smaller trees; their leaves have sharp-pointed, outward-directed teeth and are broader relative to their length. In winter, bud scales of chokecherry are brown with tan margins; other trees with similar twigs have false terminal buds. Iowa distr ibution: Native as far west as the natural lakes area in northwestern Iowa and the Missouri River in southwestern Iowa.

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Chokecherry, Prunus virginiana L. Distinguishing ch a r acter istics: Small tree or shrub, often colonial. Leaves simple, alternate, oval or obovate, 2 to 4 inches long with petioles 1/2 to 1 inch long; margins finely toothed, the tips of the teeth sharp and pointing outward; two glands normally present on petiole near the base of the blade. Winter twigs slender, glabrous, gray or red-brown; leaf scars small, halfround, with 3 bundle scars. Buds long-ovoid, 3/16 to 1/4 inch long (sometimes larger), terminal and laterals nearly equal in size; scales 6 or more, glabrous, brown with light-colored margins. Flowers similar to black cherry but commonly blooming earlier in spring; petals nearly round. Fruit a drupe 1/4 to 1/3 inch in diameter, red or dark purplish red when ripe; calyx deciduous. Bark gray, smooth. Simila r tr ees: Black cherry has narrower leaves with incurved teeth. Wild plum has its flowers in small, umbellike clusters, and its fruits are much larger. In winter, black cherry has dark red-brown bud scales; other trees with similar twigs have false terminal buds. Iowa distr ibution: Native throughout the state.

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American Plum, Prunus americana Marsh. Distinguishing ch a r acter istics: Leaves simple, alternate, oval to oblong-oval, 2 to 4 inches long with petioles 1/2 to 3/4 inch long, sharply toothed; petioles with or without glands; veins forming a network near the margins. Winter twigs slender to moderate, often thorny, gray or red-brown; leaf scars small, half-round, with 3 bundle scars. Buds ovoid, 1/16 to 1/4 (usually about 1/8) inch long, the terminal absent, often paired (side by side) above the leaf scars; scales about 6, glabrous, red or reddish brown. Flowers perfect, regular, showy, in umbellike clusters of 2 to 5, appearing with or shortly before the leaves in spring; petals 5, white, nearly round. Fruit a drupe about 1 inch in diameter, red or light purple when ripe. Bark brown or dark gray, scaly. Simila r tr ees: Cherries have nonthorny twigs, terminal buds, flowers in racemes, and much smaller fruits. In winter, distinguished from other small, thorny trees by its lack of a terminal bud and its frequently paired lateral buds. Iowa distr ibution: Native throughout the state.

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American Basswood, Tilia americana L. Distinguishing ch a r acter istics: Leaves simple, alternate, nearly round, 3 to 6 inches long with petioles 1 1/2 to 2 inches long; margins toothed; base heart-shaped and often unequal; surfaces glabrous except for small tufts of hairs in the vein axils beneath. Winter twigs moderate in diameter, gray, glabrous; leaf scars small, half-round, with 3 or more bundle scars. Buds subglobose, 3/16 to 1/4 inch long, with 2 or 3 usually bright red scales; the terminal bud absent. Flowers small, pale yellow, perfect, fragrant, in clusters of 6 to 15, appearing in early summer; each inflorescence attached to an elongate, leaflike bract that persists in fruit. Fruit a dry, globe-shaped drupe 1/4 to 1/3 inch in diameter, often persisting in winter. Bark smooth, light gray on young trees, becoming shallowly furrowed with long, narrow, parallel ridges. Simila r tr ees: Leaves of red mulberry are similar in size and shape but are somewhat longer relative to their width, with a hairy lower surface and only slightly heart-shaped base. Littleleaf linden has smaller leaves. In winter, the bright red, 2- to 3-scaled buds of American basswood are distinctive. Iowa distr ibution: Native throughout the state.

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Littleleaf Linden, Tilia cordata Mill. Distinguishing ch a r acter istics: Leaves simple, alternate, nearly round, 1 1/4 to 2 1/2 inches long with petioles 3/4 to 1 1/4 inches long; margins toothed; base heart-shaped; surfaces glabrous except for small tufts of hairs in the vein axils beneath. Winter twigs slender, brown; leaf scars small, halfround, with 3 or more bundle scars. Buds similar to American basswood but smaller, brownish. Flowers small, yellowish, perfect, fragrant, in clusters of 5 to 7, appearing in early summer; each inflorescence attached to an elongate, leaflike bract that persists in fruit. Fruit similar to American basswood. Bark smooth, gray-brown on young trees, becoming shallowly furrowed. Simila r tr ees: American basswood has larger leaves and redder buds. Iowa distr ibution: Planted throughout the state.

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Witch-hazel, Hamamelis virginiana L. Distinguishing ch a r acter istics: Shrub or small tree. Leaves simple, alternate, broadly oval to nearly round, 2 to 6 inches long, with unequal bases; margin wavy or with large, rounded teeth. Winter twigs slender, brown; leaf scars small, half-round to slightly lobed, with 3 bundle scars. Buds stalked, ovoid-elongate, naked, brown, 1/8 to 3/8 inch long, often with 2 scale-like stipules at the base. Flowers small, perfect, with long, straplike, bright yellow petals, in small clusters from the leaf axils, blooming in late autumn. Fruit a 2-celled woody capsule 3/8 to 1/2 inch long, forcibly ejecting the shiny black seeds in autumn. Simila r tr ees: This is the only tree with broad, wavy-margined leaves and bright yellow autumn flowers. In winter, pawpaw is the only other tree with naked buds. It is colonial with crescent-shaped leaf scars having 5 or more bundle scars. Iowa distr ibution: Native in counties near the Mississippi River. Occasionally planted elsewhere.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 239

Common Buckthorn, Rhamnus cathartica L. Distinguishing ch a r acter istics: Shrub or small tree. Leaves simple, subopposite (i.e., arranged in pairs at the nodes but not exactly opposite), elliptic, 1 1/2 to 2 inches long, toothed, with 3 pairs of strongly curved veins. Winter twigs slender, gray, often sharp-pointed; leaf scars small with 3 bundle scars. Buds ovoid, 1/8 to 3/8 inch long, with about 6 dark brown scales, the terminal absent. Flowers polygamous or dioecious, small, yellowish green, in small, umbellike clusters of 2 to 5 from the leaf axils. Fruit black, berrylike, 3- or 4-seeded, about 1/4 inch in diameter, persisting in winter. Bark smooth, gray, becoming scaly on larger stems. Simila r tr ees: Easily distinguished from other small trees by its subopposite leaves and buds, in autumn by its long-persisting green foliage, and in winter by its often thorn-tipped twigs. Iowa distr ibution: Naturalized across most of the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 241

Wahoo, Euonymus atropurpureus Jacq. Distinguishing ch a r acter istics: Shrub or small tree. Leaves simple, opposite, elliptic, 2 to 5 inches long, finely toothed. Winter twigs slender to moderate, green or purple, usually marked with 4 longitudinal lines; leaf scars small, half-round, with a single bundle scar forming a curved line at the top of the leaf scar. Buds ovoid, 1/8 to 3/16 inch long, colored like twigs, with 3 or 4 pairs of scales. Flowers very small, perfect, purplish, in small clusters from the leaf axils, blooming in early summer. Fruit a small pinkish 3- or 4-lobed capsule that opens in early autumn and persists on the twig all winter; seeds with red fleshy coverings, suspended by slender stalks. Simila r tr ees: Nannyberry is the only other small tree with simple, opposite, toothed leaves. It has elongate, 2-scaled buds; conspicuous clusters of white flowers; and dark purple fruits. In winter, the lined twigs of wahoo are distinctive. Iowa distr ibution: Native throughout the state.

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Nannyberry, Viburnum lentago L. Distinguishing ch a r acter istics: Shrub or small tree. Leaves simple, opposite, oval or elliptic, 2 to 5 inches long, finely toothed, with slightly winged petioles. Winter twigs rather slender, gray or red-brown; leaf scars crescent-shaped with 3 bundle scars. Buds ovoid or elongate, with 2 brown scales that meet along the edges without overlapping, the terminal 3/8 to 1 inch long and the laterals much smaller. Flowers small, white, perfect, in conspicuous clusters at the ends of the twigs, blooming in late spring or early summer. Fruit an edible dark purple drupe about 3/8 inch long, often persisting in winter. Simila r tr ees: Wahoo has lined twigs, ovoid buds with several overlapping scales, purple flowers, and pinkish fruits with bright red seeds. In winter, no other small tree has the combination of opposite leaf scars and elongate, 2-scaled buds. Iowa distr ibution: Native throughout most of the state, though common only in northeast and north central Iowa. Planted in rural areas for conservation purposes.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 245

Shingle Oak, Quercus imbricaria Michx. Distinguishing ch a r acter istics: Leaves simple, alternate, oblong or elliptic, entire, tipped by a short, slender bristle, 4 to 6 inches long with moderately stout petioles up to 3/4 inch long; upper surface dark green, glabrous, and glossy; lower surface paler and finely hairy. Buds clustered at the twig tips, ovoid, 1/8 to 3/16 inch long, slightly angled, usually hairy. Acorns hemisphere-shaped, 1/2 to 3/4 inch long, short-stalked; cups bowl-shaped with tightly appressed brown scales, covering 1/3 to 1/2 of the nut. Bark gray-brown and shallowly furrowed on lower trunk, similar to pin oak above. Simila r tr ees: Among trees with alternate, entire, unlobed leaves, this is the only one with acorns and clustered end buds. Iowa distr ibution: Native from Lee County north to Muscatine County and west to Johnson, Marion, Union, and Taylor counties, also reported from Fremont County.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 247

Osage Orange, Maclura pomifera (Raf.) Schneid. Distinguishing ch a r acter istics: Leaves simple, alternate, ovate to oblong-ovate, 3 to 5 inches long with petioles 1 1/2 to 2 inches long, entire, with milky sap; leaf surfaces glabrous. Winter twigs moderate in diameter, brown, glabrous, usually with thorns 1/8 to 1/2 inch long and short spur shoots; leaf scars small, half-round or triangular, with 3 or more frequently consolidated bundle scars. Buds globose, about 1/16 inch in diameter, the terminal absent; scales 4 or 5, brown, glabrous. Flowers green, very small, monoecious or dioecious, without petals, appearing with the leaves in spring, the staminate in racemes and the pistillate in globe-shaped heads. Fruit heavy, ball-shaped, 3 to 5 inches or more in diameter, composed of many tiny drupelike units; rind yellow-green and wrinkled, interior suffused with a milky, sticky sap. Bark orange and/or dark brown, divided into flat, often shreddy ridges separated by shallow furrows. Simila r tr ees: This is the only thorny tree with simple, broad, entire leaves. In winter, other thorny trees have larger or paired thorns. Osage orange’s many gracefully arched, bowlike branches are distinctive. Iowa distr ibution: Once widely planted for living fences and shelterbelts across southern and parts of eastern Iowa, now escaped to pastures, ravines, woods, and other uncultivated areas.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 249

Saucer Magnolia, Magnolia ×soulangeana Soul. Distinguishing ch a r acter istics: Leaves simple, alternate, obovate, 3 to 6 inches long, entire, glabrous above and more or less hairy below. Winter twigs moderate in diameter, dark red-brown or greenish brown, aromatic when cut, glabrous or sparsely hairy; stipule scars forming a ring around the twig at each node; leaf scars crescent-shaped, rather small, with a half dozen or more bundle scars. Buds ovoid; single-scaled; densely covered with long, soft greenish hairs; the terminal 1/2 to 3/4 inch long and the laterals much smaller. Flowers very large, perfect, pink, solitary at the twig tips, appearing before the leaves in spring. Fruit a conelike aggregate of small follicles, each with 1 or 2 red fleshy seeds suspended by slender filaments. Bark smooth, light gray. Simila r tr ees: Among trees with entire leaves or large, hairy terminal buds, this is the only one whose stipule scars completely encircle the twig. The large pink flowers are also distinctive. Iowa distr ibution: Cultivated across the southern two-thirds of the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 251

Pawpaw, Asimina triloba (L.) Dunal Distinguishing ch a r acter istics: Leaves simple, alternate, obovatelanceolate, 6 to 12 inches long with petioles 1/4 to 3/8 inch long, entire, thin, glabrous except when young. Winter twigs moderate in diameter, red-brown, with diaphragmed pith; leaf scars crescent-shaped, small, with 5 or 7 bundle scars. Buds densely covered with reddish brown hairs but lacking scales, globe-shaped and stalked (flower buds) or elongate and nearly sessile (leaf buds), the terminal 1/4 to 1/2 inch long and the laterals smaller. Flowers large, perfect, dark purple, appearing with the leaves in late spring. Fruit an oblong, edible berry 2 to 5 inches long and 1 to 1 1/2 inches in diameter, yellowish green when ripe in autumn, with seeds about 1 inch long. Bark smooth with small, warty thickenings, light gray to brown. Simila r tr ees: Other trees with entire leaves have longer petioles and smaller leaf blades. In winter, no other tree has nonscaly buds clothed with reddish brown hairs. Iowa distr ibution: Native in scattered localities near the Mississippi River north to Dubuque County, along the Des Moines River in Lee and Van Buren counties, in Taylor County, and in the Loess Hills in Fremont County.

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Redbud, Cercis canadensis L. Distinguishing ch a r acter istics: Leaves simple, alternate, nearly round, 2 to 5 inches long with petioles 1 to 2 inches long; margins entire. Winter twigs slender, glabrous, dark brown tinged with purple, dotted with numerous pale lenticels; leaf scars very small, raised, half-round, with 3 bundle scars. Buds dark purple, glabrous, the terminal absent and the laterals of two types: 2-scaled leaf buds about 1/16 inch long and flower buds at least 1/8 inch long with 6 or more scales. Flowers small, dark pink or white, perfect, irregular, in showy umbellike clusters of 4 to 8, appearing before the leaves in spring. Fruit a flattened pod (legume) 2 to 3 1/2 inches long, tapered at ends, often persisting through winter. Bark scaly, gray or reddish brown. Simila r tr ees: This is our only tree with nearly round, entire leaves. In winter, among trees with slender, nonthorny twigs and false terminal buds, redbud is unique in having buds of two distinct types, no stipule scars, and a legume fruit. Iowa distr ibution: Native to the southern third of Iowa, north along the Des Moines River to Boone County. Cultivated throughout much of the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 255

Northern Catalpa, Catalpa speciosa Warder Distinguishing ch a r acter istics: Leaves simple, opposite or in whorls of 3, broadly ovate, 6 to 12 inches long with petioles 5 to 6 inches long; margins entire. Winter twigs moderate to stout, brown, glabrous; leaf scars large, round with numerous bundle scars arranged in an elliptic or circular pattern. Buds globose, with about half a dozen loosely attached scales, partially embedded in the bark of the twigs and often inconspicuous; the terminal bud absent. Flowers white, splashed with lavender and yellow in their tubelike centers, perfect, irregular, 1 1/2 to 2 inches long and about 1 1/2 inches across, in large, showy panicles, appearing in early summer. Fruit a pencil-shaped pod (capsule) 6 to 20 inches long and about 1/2 inch in diameter, persisting on the tree in winter; seeds winged, with long white hairs at the tips of the wings. Bark brown or gray, separating into small, scaly plates; eventually shallowly furrowed with short, scaly ridges. Simila r tr ees: No other tree has entire leaves of this size. In winter, the large, round, opposite or whorled leaf scars and persistent pods are distinctive. Iowa distr ibution: Cultivated throughout the state, persisting in abandoned farmsteads and occasionally escaping to stream banks, roadsides, and waste places.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 257

Japanese Tree Lilac, Syringa reticulata (Blume) Hara. Distinguishing ch a r acter istics: Leaves simple, opposite, broadly ovate, 2 to 5 1/2 inches long, entire. Winter twigs rather slender, greenish brown or brown; leaf scars small, shield-shaped, raised, with a single bundle scar forming a fine broken line. Buds subglobose, about 1/8 inch long, with 4 to 6 pairs of light brown scales. Flowers perfect, white, in large, showy, terminal panicles, blooming in early summer. Fruit a 2-celled, thin-walled pod (capsule) about 3/4 inch long, splitting open at maturity and remaining on the twig all winter. Bark rather smooth, dark gray, with prominent white lenticels, eventually separating into small plates. Simila r tr ees: This is the only small tree with opposite, broadly ovate, entire leaves. In winter, the cherrylike bark and small, persisting seed pods distinguish this from other small trees with opposite leaf scars. Iowa distr ibution: Occasionally planted throughout the state.

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 259

Russian-olive, Elaeagnus angustifolia L. Distinguishing ch a r acter istics: Leaves simple, alternate, linear to oblong-lanceolate, 1 1/2 to 5 inches long with petioles 3/16 to 3/8 inch long; margins entire; upper surface dark green and dotted with minute silver-gray scales, lower surface shiny silver-gray. Winter twigs slender, dark brown, covered by minute silver-gray scales, often bearing short thorns; leaf scars very small, half-round, with 1 bundle scar. Buds globose to short-ovoid, 1/16 to 1/8 inch long, gray-brown to silver-gray, with 4 visible scales. Flowers small, perfect or imperfect, yellow on inside, apetalous, solitary or in clusters of 2 to 4 from the axils of the leaves, appearing in early summer. Fruit oblong-ovoid, about 3/8 inch long, drupelike with a mealy flesh, yellow with a covering of minute silver-gray scales, ripening in early autumn and persisting on the tree in winter. Bark light gray; separating into long, vertically oriented, often shreddy strips; eventually furrowed with flattened ridges. Simila r tr ees: No other tree has minute silvery scales on its leaves, twigs, and fruits. Iowa distr ibution: Planted throughout the state and occasionally escaping to uncultivated areas.

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d e s c r i p t i o n s o f t r e e s p e c i e s 261

Dogwoods, Cornus L. Distinguishing ch a r acter istics: Shrubs or small trees. Leaves simple, opposite (alternate in one species), entire; veins curving upward and following the margin. Winter twigs slender, brightly colored in some species; leaf scars small, raised, crescent- or U-shaped, with 3 bundle scars. Buds stalked, ovoid to somewhat elongated, with 2 scales that meet along the edges. Flowers (of native species) small, white, perfect, in terminal corymblike clusters, blooming in late spring or summer. Fruit a small white or blue drupe. Simila r tr ees: Among woody plants with opposite, entire leaves, dogwoods are unique in having strongly curved veins that follow the margins. In winter, they are easily distinguished from other woody plants by the combination of stalked, 2-scaled buds and raised, crescent- or U-shaped leaf scars. Iowa distr ibution: Native throughout the state (see the discussion in part 2).

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Y d e s c r i p t i o n s o f t r e e s p e c i e s 263

Honeysuckles, Lonicera L. Distinguishing ch a r acter istics: Shrubs, occasionally singlestemmed and somewhat treelike. Leaves simple, opposite, entire, small, shortpetioled, with straight or slightly curved veins. Winter twigs slender, with the previous year’s bud scales persisting at their bases; leaf scars small, raised, with 3 bundle scars. Buds variously shaped, rather small, with several scales in common species, the scales arranged in 4 vertical rows. Flowers small, perfect, usually white or pink, paired at the ends of short stalks from the leaf axils, blooming in spring. Fruit a small red or orange berry, often persisting on the twig in winter. Simila r tr ees: Honeysuckles are easily distinguished by their small, entire-margined leaves, which are usually less than 3 inches long, and their paired flowers and fruits. In winter, other large shrubs with opposite leaf scars have 2-scaled buds (dogwoods, nannyberry) or lined twigs (wahoo). Common buckthorn, which frequents the same habitats as honeysuckles, has subopposite leaf scars. Iowa distr ibution: Naturalized across most of the state.

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Part T wo

The Natural History and Uses of  Iowa’s Trees

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At the time of European American settlement, conifers grew mostly on rocky bluffs and steep slopes in wooded valleys. Today they can be found almost everywhere in Iowa.

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Conifers Tr ees th at h ave needlelike leaves and regular whorls of branches, with the trunk running straight and unforked to the top of the crown, are often called evergreens, although some lose their leaves in autumn and are not really “ever green.” Because these trees produce their pollen and seeds in cones, botanists prefer to call them conifers, which is Latin for “cone-bearing.” Both the pollen and seed cones occur on the same tree, except in the junipers. Appearing with the new growth in spring, the cones are often brightly colored at first. The male cones fall to the ground after shedding their pollen, but the female cones continue to develop and may remain on the tree for several years. Conifers are the largest and most important branch of an ancient line of seed plants called the gymnosperms. Yews and the ginkgo, which are planted as ornamentals in Iowa, represent two other branches of the gymnosperm line. Representatives of other gymnosperm lines occur in deserts and tropical forests, and others are known only from fossils. Conifers are a prominent part of the landscape in Iowa today, but this was not always so. When the settlers arrived in Iowa from the east, only three coniferous trees occurred here — white pine, redcedar, and balsam fir. The redcedar was distributed along river bluffs throughout most of the state, though in smaller numbers than today; the other two species were native to northeastern Iowa. Most of the conifers found in Iowa today were introduced from Europe, the Rocky Mountains, and the Great Lakes region. In Iowa, conifers are valued for landscaping, windbreaks, wildlife plantings, and reforestation and as Christmas trees. Their seeds are eaten by many kinds of birds and small mammals, and their foliage is an important source of winter cover. In the discussion below, the species are arranged alphabetically by their genus name.

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268 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s

The white or concolor fir is useful for land­ scaping and windbreaks in Iowa.

Firs, Abies Mill.

Balsam Fir, A. balsamea (L.) Mill. White or Concolor Fir, A. concolor (Gord. and Glend.) Lindl. Fraser Fir, A. fraseri (Pursh) Poir. Firs, like their close relatives the spruces, are trees of high mountains and cold, northern regions. There are about forty species, including nine in North America. With their tall, symmetric, and spirelike crowns, they stand out in the places where they grow. Unfortunately, most species of firs are sensitive to heat and drought, so one does not see many of these beautiful trees in Iowa. One species that does grow well here is the white or concolor fir, which comes from the Rocky Mountains. Its dense bluish green foliage and neat, conelike habit make it popular for land-

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c o n i f e r s 269

scaping, windbreaks, and Christmas trees. White fir can grow quite large, but dwarf cultivars are available for gardens. Another species, the balsam fir, is native across most of Canada and the northeast United States, barely ranging into the northeast corner of Iowa. It is common and widespread in our northern Great Lakes states, but in Iowa it grows only on steep, north-facing bluffs, which remain relatively cool and moist in summer. One of the best places to observe it is along the Upper Iowa River at Bluffton, in northern Winneshiek County. Fraser fir, native to the southern Appalachians, is planted in Iowa for Christmas trees. It resembles balsam fir except for its cones, which have long, reflexed bracts that protrude between the scales. Other species of firs are being tested at arboretums in Iowa, with the hope that some might prove useful for landscaping. The Douglas-fir, which is planted across most of the state, is not closely related to the true firs (see page 279). Firs resemble the more common spruces, so if you found one, how would you identify it? Perhaps the easiest way is to place a leaf between your finger and thumb and try to roll it. Spruce leaves are squarish in cross section and roll easily, while the flat leaves of firs do not. Cones are also helpful when they are present. Spruce cones hang down from the branches and, when they fall, remain intact. Fir cones point upward and disintegrate when mature.

Eastern Redcedar, Juniperus virginiana L. The redcedar is one of our most tenacious and adaptable trees. Across its broad range in Iowa, the cedar clings to rocky cliffs, colonizes eroded and overgrazed land, and thrives in almost any kind of soil. It is the only wild conifer throughout most of the state. Botanically speaking, the redcedar is a juniper. As in other junipers, and unlike most conifers, its male and female cones occur on separate plants. The male cones overwinter on the twig tips, then open and shed their pollen in spring. After the female cones are pollinated, they become fleshy and berrylike. These juniper “berries” are an important food for wildlife. Many familiar songbirds relish them, including the cedar waxwing, robin, and bluebird. The hard seeds pass through the birds unharmed, propagating the species. Though rooted in the ground, redcedar truly travels by wing. While hardy and tough, redcedar is intolerant of both fire and shade. It is far more abundant today than when Iowa was settled, because wildfire is no lon-

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270 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s ger a threat. From its presettlement homes on ridges and cliffs, where fire never reached, the cedar has spread far and wide. Some of those original cliffside cedars are alive today, Iowa’s oldest native trees. A few, along the Cedar River in Linn County, are more than four centuries old. These ancient trees are not nearly the size one might expect, much smaller, in fact, than most trees in the woods nearby. If you watch redcedars in spring, you may notice something odd. Knobby red-brown galls, the “fruit” of a rust disease, suddenly come to life when it rains, forming gelatinous “tails” that protrude from the twigs. Though alarming to see, these are not really harmful to the tree. The tiny spores inside are spread by the wind, where they infect the leaves of apples and crabs. The distinctive red-brown heartwood of the redcedar is hard and moderately heavy, valued for chests, wardrobes, and closet linings because of its fragrance and reputed ability to repel moths. Cedar’s natural durability also makes it useful for fence posts. Redcedar has numerous cousins that are used for landscaping. These vary considerably in habit, from trees to shrubs to ground covers. Many of the larger types are cultivars of the Chinese juniper, J. chinensis L. Like the red­ cedar, this and other species are tough, adaptable plants that will grow almost anywhere, except where the soil is very wet. They do best in full sun. Two low, shrubby junipers are native in Iowa, though confined mostly to the northeastern part of the state and not common. These are the common juniper, J. communis L. var. depressa Pursh, and the creeping juniper, J. hori­ zontalis Moench. Look for them in dry prairies and open woods on bluffs and slopes.

European Larch, Larix decidua Mill. The European larch, a conifer with deciduous leaves, has as many faces as there are seasons. In winter it is as bare and lifeless as any broadleaf tree, but its tall, tapered trunk and horizontal branches are distinctly coniferous. When spring arrives, its branches are decorated with tiny bright red cones, which nicely complement the soft light green leaves that emerge from the buds. In summer the larch’s foliage takes on a darker hue, and it resembles other conifers, but its drooping twigs and slender leaves give it a distinctive look. Finally, in early November, after most broadleaf trees have lost their leaves, the larch turns a brilliant gold, providing a last blaze of color before the onset of winter.

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The European larch is a deciduous conifer whose leaves turn golden-yellow in autumn.

In Iowa, European larch is useful for both landscaping and conservation plantings. It grows faster than many other conifers, often exceeding a height of 40 feet in 20 years. It is also wind-firm, relatively free of disease and insect problems, and fairly adaptable as to soil. Poorly drained sites or droughty sites should be avoided. The larch is native to the mountains of central and eastern Europe and has been widely planted in Europe and the United States. Its wood is hard, heavy, strong, and durable. The related tamarack or eastern larch [L. laricina (Du Roi) K. Koch] is occasionally planted in Iowa, but it is a less graceful tree. It is native to the coniferous forests of Canada and the northern United States, where it is a common inhabitant of bogs.

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Spruces, Picea A. Dietr. Norway Spruce, P. abies (L.) Karst. White Spruce, P. glauca (Moench) Voss. Blue Spruce, P. pungens Engelm. Spruces are among the hardiest and most adaptable conifers. Admired for their dense, symmetrical forms and handsome foliage, they are widely planted in Iowa for windbreaks and landscaping. Like their cousins the firs, which they closely resemble, spruces are trees of northern and mountain forests. None is native to Iowa, which seems odd considering how well they grow here. Three species are commonly planted. The largest of these, the Norway spruce, was imported from Europe many years ago. It is the fastest-growing and most attractively shaped of the three, developing long, drooping branches as it matures. More than a hundred cultivars have been selected and introduced, including trees that are columnar, weeping, and dwarf in habit. Where space is limited, the smaller forms are good choices for landscaping. Blue spruce, which is native to the Rocky Mountains, is the favorite species for ornamental use. Its attractive blue color is caused by a white waxy material on the surface of its leaves, which eventually weathers off on the older, inner foliage. The intensity of this color varies greatly from one tree to the next, with trees grown from seed sometimes green like other spruces. To ensure uniformity in color, many of the trees sold in nurseries are propagated by grafting. As in other spruce species, dwarf forms are available for gardens. When planting a blue spruce, remember that a tree so striking — and eventually so large — should be placed carefully, so it does not detract from other plants and block important views. Ample spacing between trees is important, too, because blue spruces that are crowded may be more susceptible to canker and other diseases, as discussed below. White spruce is not so colorful, but it too is a handsome tree. Its dense foliage and ability to withstand extremes of heat and cold make it desirable for windbreaks as well as landscaping. A variety called the Black Hills spruce is an attractive, conical tree that is somewhat smaller, more compact, and slowergrowing than typical white spruce. White spruce is native to the coniferous forests of Canada and the northern United States. Its wood is moderately light and soft, even-grained, easily worked, and strong for its weight. Pulp and lumber are important uses.

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Blue spruce is admired for its striking foliage, but the intensity of its color varies greatly from tree to tree, with some being more green than blue.

Spruces are usually trouble-free, but they can be injured by diseases and insects when stressed by old age, poor drainage, overcrowding, or drought. Spider mites can be a real nuisance, especially on the Dwarf Alberta spruce, a commonly planted form of the white spruce. The most widespread and serious diseases are canker, which kills the branches, and needle-cast, which causes the older, inner needles to turn purplish brown in autumn and then drop the next spring. Both of these diseases, which are caused by fungi, usually start near the base of the tree and progress upward. A new problem, called sudden needle drop, is also causing concern. The older, inner needles of affected trees suddenly turn yellow or brown and then fall, leaving only the new growth at the tips of the branches. Affected branches may appear at various heights in the tree, causing scattered bare areas. As this book goes to press, the cause of this condition is not yet known. For updated information, go to www.extension.iastate.edu. Diseases like these are not easy to control, and an ounce of prevention may be worth a pound of cure. To keep spruces in the best of health, plant them

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274 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s in a sunny location where the soil is neither very dry nor very wet. Mulch the ground underneath the trees and, if possible, water during times of prolonged drought. If branches become diseased by canker — as evidenced by dieback and accumulations of dried white sap — remove and destroy them when the weather is dry. Avoid wounding the trees or compacting or disturbing the soil around their roots. To see new spruces that may be useful in Iowa, visit one of Iowa’s arboretums. See part 5 of this book for locations and contact information.

Pines, Pinus L.

Eastern White Pine, P. strobus L. Red Pine, P. resinosa Ait. Austrian Pine, P. nigra Arnold Ponderosa Pine, P. ponderosa Laws. Scots Pine, P. sylvestris L. Mugo Pine, P. mugo Turra. Jack Pine, P. banksiana Lamb. Virginia Pine, P. virginiana Mill. To many people not so familiar with trees, the words “pine” and “evergreen” mean exactly the same thing. Pines are actually just one group of evergreens (or conifers, as they are more properly known). Considering how abundant pines are, however, one can understand the confusion. Pines are seen everywhere in Iowa today, but this was not always so. When white settlers arrived in Iowa from the east, there was only a single species here, and it had a very limited range. Our other pines were introduced from Eurasia, the northern United States, or western North America. As a group, pines are easy to recognize. Unlike spruces, firs, and other trees bearing “needles,” the leaves of pines are grouped in small bundles called fascicles. Each fascicle has from two to five leaves, depending upon species. The length, thickness, and color of the leaves vary considerably from one species of pine to the next. Pines’ relatively large and woody cones are also distinctive. These differ so much among species that one can identify a pine from its cone alone, without seeing the tree. The cones of white pine mature in a single season as in most other conifers, but those of most Iowa pines do not mature until the end of their second year.

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Many kinds of pines can be used for landscaping and conservation in Iowa, but only half a dozen are commonly planted. Though hardy and adaptable, all share the need for ample sun and good drainage. Proper spacing is also important, especially for the longer-leaved species, which are prone to needle-blight diseases under crowded and humid conditions. For suggestions on some unusual species to try, see pages 379–381. Iowa’s only native pine, the eastern white pine, is one of America’s most historic and celebrated trees. When Europeans first came to America, giant white pines were abundant and widespread in the Northeast and the Great Lakes states. Their numbers were quickly depleted to satisfy our nation’s demand for wood, dramatically changing the landscape and ecology. Majestic trees Pine “flowers” are actually small cones. The male cones (left) are arranged in tight clusters and fall to the ground after releasing their pollen. The female, which are often red when they first appear, grow larger and produce seeds.

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276 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s 150 feet tall were felled, transported south on rivers and streams, and used for everything from lumber and shingles to furniture and paneling. When settlers arrived in Iowa, white pine was confined largely to the northeastern corner of the state, with outlying populations in central and southeastern Iowa. It has since proved popular for landscaping, windbreaks, wildlife plantings, and reforestation and has been planted throughout the state. Dwarf, columnar, and weeping cultivars are available for landscape use. White pine is perhaps the easiest pine to identify, both up close and from a distance. Its slender leaves occur in fascicles of five, instead of two or three as in other common species, and have a softer look and feel. Its elongate cones are another distinctive feature. When viewed from a distance, white pine can be easily recognized by its irregular shape. Most pines have a fairly symmetric crown that tapers from the bottom to the top, with branches of gradually decreasing length. In white pine, the limbs may vary considerably in length from one whorl to the next, especially in old trees.

White pine often towers high over the forest canopy and is easily recognized by its distinctive silhouette.

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Red pine is one of three long-needle pines that are commonly planted in Iowa. Many people call it Norway pine, although it is native to northeastern North America, not Europe. The state tree of Minnesota, it is a conspicuous feature of the northern lakes region where so many Iowans go to vacation and fish. Here it is seen most often in conservation plantings, less often in town. Like other northern trees, it is best planted in a moist site protected from hot summer winds. Austrian pine, another long-needle tree, was introduced from central and southern Europe and has long been popular for landscaping and highway beautification. Among the most adaptable of pines, it will grow in clay soils and resists salt, heat, drought, and urban conditions. Unfortunately, Austrian pine also has its limitations, including its susceptibility to needle blights and Zimmerman pine moth, which can damage the appearance of trees and shorten their lives. The Iowa pine with the longest leaves — up to 11 inches — is the Ponderosa pine. Native to the western United States, it has proved useful for landscaping and conservation plantings in western Iowa. It is often less successful in the eastern part of the state, where the more humid climate favors needle-blight diseases. Among our shorter-needle pines, the handsome Scots pine is the most distinctive, with its bright orange upper bark and often picturesque habit. Native across most of the Eurasian continent, it has been widely planted in Iowa for shelterbelts, farm groves, conservation purposes, and landscaping. Unfortunately, pine wilt has been killing all but the smallest trees, limiting the value of Scots pine to Christmas trees and other temporary plantings. Mugo pine is a dwarf among pines, though not always tiny — individuals can grow 30 feet tall and just as wide. Mugo also tends to develop multiple stems, resembling a shrub in habit as well as size. Where space allows, it is a nice addition to landscapes and gardens. It is native to the mountains of central and southern Europe. Two other short-needle pines are useful for conservation plantings in Iowa, especially on sandy soils, eroded areas, and other difficult sites. Virginia pine has adapted well to coal spoils in southern Iowa, even reproducing from seed, while jack pine is grown statewide. Jack pine is native to the northern United States and Canada, ranging farther north than any other pine. Virginia pine comes from the Appalachian Mountains. Wherever they grow wild, pines are important timber trees. The species

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Scots pine is notable for the bright orange bark of its upper trunk and branches.

have overlapping but somewhat different uses, depending on the properties of their woods. White pine is relatively light and soft and is straight-grained and easily worked. It shrinks and swells very little, making it ideal for foundry patterns, doors, and window sashes. Red pine is somewhat heavier and harder, useful for poles, pilings, landscape timbers, general construction, millwork, and pulp. Ponderosa pine is used for construction, millwork, interior finish, and other purposes. Pines are also useful to wildlife, both for their evergreen cover and for food. Their seeds are eaten by many birds, including chickadees, nuthatches, finches, and the red-bellied woodpecker. Pines rank second to oaks in their overall value to wildlife. Though hardy and adaptable, pines as a group have many diseases and insects. White pine is fairly trouble-free, at least in Iowa, but other pines are more problematic. Some pests are life-threatening, others more of an aesthetic concern.

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The most serious problem is pine wilt, which is caused by a combination of pine wood nematodes, blue-stain fungi, bark beetles, and unfavorable environmental conditions. The foliage of infected trees turns gray-green and then brown, and the trees die quickly. Scots pine more than 10 years old are most commonly affected, but individuals of other species are sometimes killed. There is no cure, but spread of the disease can be slowed through proper cultural practices and by promptly removing and destroying dead trees. Zimmerman pine moth also attacks several species of pine, but it is mostly commonly seen on Austrian, red, and Scots pines. Damage is caused by the insect’s larvae, which bore into shoots, branches, and trunks, feeding on the inner bark and sapwood. Infested shoots turn brown and die, curving downward to form a shepherd’s crook. When larger stems are invaded, masses of white pitch appear on the bark, especially where the branches join the stem. Control is accomplished by pruning infested wood or by spraying an insecticide on the bark while the larvae are present, usually in mid April and mid August. Since the moths often concentrate their feeding on certain trees, it may be helpful to remove and destroy these. Long-needle pines such as Austrian and Ponderosa are also afflicted by various needle-blight diseases caused by fungi. These cause the leaves to turn brown and die, and in severe cases they may cause extensive defoliation and dieback. To prevent the disease, trees should be planted in open locations where sun and wind help keep the foliage dry. Fungicidal sprays can protect existing trees, but they must be timed carefully and repeated annually to achieve good results. For assistance in diagnosing and treating a tree, contact your local extension office.

Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco This handsome conifer is not a fir at all, though its leaves resemble those of its namesakes. It is native to the western United States, where it occurs in two distinct forms, Rocky Mountain and Pacific Coast. Trees from the Rocky Mountains, which are adapted to a much colder, drier, and more extreme climate overall, are useful for planting in Iowa. In form the Douglas-fir resembles the blue and white spruces, with bluegreen foliage and a compact, pyramidal crown. Growth rate in Iowa is moderate, with trees maturing at a height of 40 feet or more. Although usually rather trouble-free, it is sometimes attacked by needle-cast and canker.

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Needle-blight diseases can cause dieback and decline in longneedle pines, especially Austrian pine (shown here) and ponderosa pine.

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Douglas-fir is one of the most important timber trees in the United States, especially the large trees of the Pacific Northwest. Its wood is used for lumber, plywood, mine timbers, poles, fencing, laminated beams, and millwork. Another important use of this valuable tree is for Christmas trees, especially in the West.

Baldcypress, Taxodium distichum (L.) Rich. A conifer from the southern swamps might seem ill-suited to planting in Iowa, but the baldcypress grows very well in the warmer parts of the state, and not only in wet sites. There are anecdotal reports of trees in Minnesota, and the species should be tried in northern Iowa. Seed sources from the northwest part of the range in Illinois and Indiana are especially worthy of trial. Baldcypress is among the few conifers that are deciduous. Its soft, ferny leaves are light green in summer, then turn orange-brown in autumn. Cultivated trees are narrowly to broadly pyramidal in habit and grow to 60 feet or more. They may or may not produce the distinctive “knees” of wild trees, peculiar outgrowths of the roots whose function is not understood. Baldcypress is native to swamps in the southern United States but grows well when planted in Iowa.

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Yews, Taxus L. Yews are among the most beautiful of conifers, and because of their bushy habit and tolerance of pruning, they are prized for landscaping. Though adapted to varied sites, they are intolerant of soils that are poorly drained or very dry, and winter injury can be a problem where exposed to wind and sun. Shrubby but not dwarf, they can become small trees and overgrow the space where they’re planted. Cultivated yews are Eurasian in origin, but Iowa does have a native species, the Canada yew (T. canadensis Marsh.). A prostrate shrub only 2 to 3 feet high, it grows on rocky bluffs and moist wooded slopes in eastern Iowa. Deer love both native and cultivated species and have killed or severely damaged our native plants in more accessible locations.

Arborvitae or Northern White Cedar, Thuja occidentalis L.

No one is certain why this handsome tree was named arborvitae, a Latinized form of the French l’arbre de vie or “tree of life.” Some credit the tree’s longevity, which may exceed 400 years. Others cite a sixteenth-century story in which a tea brewed from the tree’s bark and leaves cured scurvy in early explorers. A third possibility is the tree’s evergreen foliage — evergreens have long symbolized eternal life and are frequently planted in cemeteries. Arborvitae is valued for landscaping in Iowa and sometimes planted in farm windbreaks, especially in the northeastern part of the state. With its dense foliage, relatively slow growth, and tolerance of pruning, it is a good choice for hedges and screens. Cultivars of varied sizes and shapes are available, including some that are dwarf and rounded, useful for small gardens and foundation plantings. Arborvitae is an adaptable tree and one of the few conifers that tolerates wet sites. Though hardy and relatively free of diseases, it is susceptible to winter injury when planted in dry locations. Deer favor its foliage and can do severe damage during the winter months. The natural range of the arborvitae includes the Great Lakes states, New England, and southeastern Canada. It has escaped from cultivation in a few sites in northeastern Iowa, where it can be seen on seepy limestone road cuts.

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Arborvitae is popular for landscaping and is also desirable for screens and windbreaks.

Where native, it grows in a variety of sites but is most commonly found in swamps, along lakeshores, and in similar moist habitats, often forming thickets. Wild trees grow 40 to 50 feet tall with an oval to oblong crown and are often multiple-stemmed. Foresters know the arborvitae as the northern white cedar. The word “cedar,” like “fir” and “pine,” is used for several trees that are not closely related. Trees called cedar in the United States belong to the cypress family, a group characterized by tiny, scale-like, evergreen leaves and soft, light, durable, aromatic wood. Other cedars, including the famed cedar of Lebanon, belong to the genus Cedrus of the pine family. They have tufted, needlelike leaves resembling those of larches. The wood of the arborvitae is used for fencing, poles, shingles, lumber, and various novelty items. Native Americans valued it for the frames of their canoes because it is easy to split and work, resists decay, and is very light in weight.

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Eastern Hemlock, Tsuga canadensis (L.) Carr. With its small dark green leaves and irregular habit, hemlock is one of our most attractive and distinctive conifers. Though hardy throughout Iowa, it is sensitive to heat and dryness and best adapted to the eastern part of the state. Dwarf types are available for landscaping. Hemlock is native to the northeastern United States and southeastern Canada. Unfortunately, it is dying out through large parts of its range from an introduced insect pest, the hemlock woolly adelgid.

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Flowering Trees Flow er ing tr ees, a much larger group than the conifers, account for most of the tree species native to Iowa. These trees provide shade for our homes, fuel for our fireplaces, lumber for our furniture, and much of our locally grown fruit. Their colorful blossoms liven the landscape in spring, and their turning leaves are much admired in autumn. If asked to name a flowering tree, most people would say redbud, magnolia, crabapple, or other tree with conspicuous, brightly colored flowers. Other trees bear flowers too, though the blossoms are often overlooked. In fact the flowers of most trees are small, drab, and inconspicuous, borne high above the ground in spring. Many of these are pollinated by wind, so they don’t need to be large and showy. Flowering trees are also called broadleaf or deciduous trees, referring to their foliage. Their leaves come in a great variety of shapes and sizes, but all are much broader than those of conifers. They also differ from conifer needles in having a conspicuous network of vascular bundles, commonly called veins. These structures serve as the “plumbing” of the leaf, transporting water and mineral nutrients into the leaf and sugars out of it. In Iowa the flowering trees are all deciduous, but in warmer climates some retain their leaves throughout the year. If you travel to our southern states in winter, you have undoubtedly seen the evergreen magnolias, hollies, and live oaks there. If you visit the tropics, you will see even more broadleaf evergreen trees. Flowering trees are also called hardwoods because their wood, on average, is harder and heavier than that of the conifers or softwoods. In some species, though, including the cottonwood and basswood, the wood is considerably lighter and softer than some conifers. A more reliable distinction is the presence of vessels or “pores” in the wood of flowering trees. Coniferous wood never has vessels. Another common feature of flowering trees is the production of fruit. Botanists define a fruit as the ripened, seed-bearing ovary of a flower. Not all fruits are fleshy and edible like an apple or plum. The pods of the locust are fruits

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286 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s too, as are the acorns of oaks, the “seeds” of maples, the nuts of walnuts and hickories, and the tiny capsules of the cottonwood. In the discussion below, the species are arranged alphabetically by their genus name.

Maples, Acer L. Sugar Maple, A. saccharum Marsh. Black Maple, A. nigrum Michx. f.   [A. saccharum var. nigrum (Michx. f.) Loud.] Norway Maple, A. platanoides L. Silver Maple, A. saccharinum L. Red Maple, A. rubrum L. Freeman Maple, A. ×freemanii Murray Boxelder, A. negundo L. Mountain Maple, A. spicatum Lam. Amur Maple, A. ginnala Maxim. Japanese Maple, A. palmatum Thunb. The maples are among Iowa’s most common and important trees. They grow everywhere in the state, from streets and yards to riverbanks and forests. Six species are native here and several more are planted. Our most familiar maples are medium-size to large trees. They are commonly divided into two groups, the hard maples and the soft maples. These names refer to the relative hardness of their woods, but there are also differences in foliage and flowers. Hard maples have leaves with few or no teeth along the margins and long-stalked, greenish flowers that appear just before the leaves in mid spring. Soft maples have toothed leaves and red or reddish short-stalked flowers that appear long before the leaves in early spring.

Hard Maples Hard maples in Iowa include the sugar, black, and Norway maples. The first two are very closely related and considered by some botanists to be varieties of a single species. Norway maple resembles them in leaf but has distinctive flowers, fruits, and bark, as discussed below. The sugar maple is named for its sweet sap but is perhaps best known for its striking autumn color. The green in its leaves begins to fade as the days

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The leaves of black maple form a yellow carpet when they fall in autumn.

shorten in September, and by mid October its crown is aglow with orange, red, and yellow. It is no coincidence that the northeastern corner of Iowa, which has the largest concentration of sugar maples in the state, has the reputation for the most spectacular autumn color! Black maple colors similarly though it is often more yellow than red. It covers the same range as sugar maple in eastern Iowa but extends farther west and is the predominant hard maple in central Iowa. The two species have similar ecological requirements and are most commonly found on north- and eastfacing slopes with red oak and basswood. They hybridize when they occur together, producing trees with intermediate characteristics. Both species are excellent shade trees where the soil is well drained and fertile. They develop dense, rounded to oval crowns and typically reach heights of 60 feet or more. Black maple tends to grow more slowly when young, but as one might expect from a tree that ranges farther west, it seems better adapted to Iowa’s hot, dry summers. The cultivar ‘Greencolumn’ is of Iowa origin, selected by nurseryman Bill Heard from a native tree in Boone County.

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Norway maple is often used for landscaping in Iowa. Cultivars with purple or purplish foliage are especially popular.

Sugar and black maples are also important commercially. The sap of both species, especially the sugar maple, is tapped in late winter and boiled to make maple syrup. Their wood is valued for its strength, hardness, attractive light color, and resistance to abrasion. Important uses include flooring, furniture, cabinets, charcoal, musical instruments, and bowling pins. A European hard maple, the Norway maple, has probably been more widely planted in Iowa than any other introduced tree. It has been cultivated in Europe for centuries, and a great many cultivars are available, including some with colorful spring or summer foliage. These include ‘Schwedler,’ whose leaves are purple in spring, and ‘Crimson King,’ with purple leaves all season. Norway maple normally develops a broad, rounded crown; it matures at a height of 40 to 60 feet but can grow much larger. Autumn color varies among cultivars and individuals, but trees with green summer foliage usually turn yellow. This species is among the last trees to turn in fall, often as late as November. Norway maple is usually trouble-free and easy to grow, but it is not entirely

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free of problems. Young trees may develop frost cracks when exposed to winter sun, and girdling roots can cause decline on larger and apparently established trees. Trees stressed by drought and injury may be damaged by verticillium wilt. This species has invaded woodlands in several eastern states and should be watched for invasiveness in Iowa, particularly in the eastern part of the state, where its similarity to native sugar maple will make it difficult to detect. Among maples, Norway maple has some of the most interesting flowers. Though drably colored, these are larger than those of other maples and produce a distinctive sweet fragrance. They usually appear in April as the leaves are just developing.

Soft Maples Soft maples in Iowa include the silver maple, red maple, and hybrids between the two. Silver maple is native throughout the state and widely planted. Red maple grows over a broad range in the eastern United States and Canada and is planted in Iowa as an ornamental. Silver maple is named for the pale undersurface of its leaves, which gives the tree a silvery appearance when viewed from a distance on windy summer days. Iowans have long appreciated this tree for its fast growth, adaptability, and handsome appearance, planting it along their streets and next to their homes. It is one of our largest native trees, attaining a height of at least 60 and often 100 feet. The crown is typically broad and rounded, at least two-thirds as wide as the tree is tall. Autumn color is usually yellow but can be orange under good conditions. Silver maple can grow as fast as 2 to 3 feet per year when young, but like other fast-growing trees, it has relatively weak wood and thus is more easily damaged in storms. This is the main limitation of a tree that is otherwise free of serious problems and is reasonably long-lived. Other troubles include tar spot (large black patches on the leaves), cottony maple scale (frothy white fibers on the twigs and a sootlike discoloration of the leaves), maple bladder gall (small red or black bumps on the leaves), and maple spindle gall (slender red outgrowths from the leaves). These can be alarming to homeowners when abundant but seldom cause permanent damage to the trees. Silver maple is a true harbinger of spring, being the first of our native trees to bloom. Its bright red flower buds, which are grouped in clusters on the twigs, swell and open as early as March. Few people notice the tiny apetalous

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Admired for its fast growth and attractive foliage, silver maple is a common shade tree in Iowa.

blossoms within. The male and female parts occur in separate flowers, and individual trees usually have mostly one or the other, although it is not uncommon to find both types on a single tree. The seeds follow quickly, providing the familiar helicopters that so delight children (but when abundant, bedevil adults). In nature, silver maple is a common inhabitant of lakeshores, riversides, and bottomland forests. Its early-maturing seeds are an adaptation to this habitat, which often floods in spring and early summer. The resulting deposits of silt and sand make a perfect seedbed for this pioneering, sun-loving tree. The silver maple’s close cousin, the red maple, is known for its beautiful red and purple-red fall color. It can also be quite attractive in early spring, with its

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small red flowers and young fruits. Red maple has been widely planted in Iowa, and a wild population in Allamakee County is believed to be native. Red maple grows best in acid soil and may develop chlorosis when planted elsewhere. It often hybridizes with silver maple, producing offspring with intermediate characteristics. The best of these combine the vigor and adaptability of silver maple with the autumn color of the red. Cultivars include ‘Armstrong,’ ‘Celzam’ (Celebration), ‘Jeffersred’ (Autumn Blaze), and ‘Marmo.’ Botanists group all these under the name Freeman maple. Both the hard and soft maples share a characteristic that can be troublesome to homeowners. Lawn grasses often grow poorly beneath them because their dense crowns and aggressive roots reduce light and moisture. Light can be increased by removing lower branches and thinning the crown, but root competition is difficult to combat. An alternative to fighting the problem is to turn it into an opportunity, by mulching bare areas under the tree and experimenting with wildflowers and groundcovers.

Boxelder Another native maple, the boxelder, does not have “maple” in its name and would not be recognized as a maple by most people, as its leaves are quite different. It does have the typical maple fruit, however, and in winter looks much like other maples. Its sap can even be used to make maple syrup! Unlike the other maples, boxelder has a poor reputation and is not much planted. It is a less attractive tree, is prone to storm damage, is relatively shortlived, and has little fall color. It is also a favorite (but not the only) host of the boxelder bug, which can become a nuisance when it invades homes in the fall. In nature the boxelder is weedy, invading open areas and even woods, displacing more valuable trees. The people who settled Iowa’s prairies, however, viewed this species differently. They needed trees for shade, shelter, and fuel and did not have access to the variety of plants we have now. The native boxelders that grew along the rivers and streams fit their needs very well, for the boxelder grows extremely fast, is not fussy about soils, and withstands extremes of drought, heat, and cold. Even today, the boxelder does have its uses. It can be planted as a temporary screen or windbreak in places where better trees do not grow well. It is also a useful tree for wildlife, as its seeds persist on the branches throughout winter and provide nourishment when other foods are scarce. The seeds are espe-

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A mature boxelder tree at Iowa Lakeside Laboratory.

cially sought by evening grosbeaks, whose occasional invasions of Iowa and other midwestern states are usually correlated with a poor crop of boxelder seeds in their usual range to the north.

Small Maples Our familiar maples are all substantial trees, but of the more than one hundred maple species worldwide, many grow no larger than a crabapple. One of these is native in Iowa, and two are commonly planted. Several others show potential as ornamental trees. Mountain maple ranges throughout the northeastern United States, Great Lakes region, and adjacent Canada, reaching the edge of its range in extreme northeastern Iowa. Here it occurs only on steep, moist, north- and east-facing slopes where conditions are very cool in summer. It is a true wildling, not thriving when planted outside this restricted habitat. Amur maple, from northeastern Asia, is shrubby in habit and usually no

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more than 15 to 20 feet tall. Hardy, adaptable, and easy to grow, with fiery red fall color and seeds that persist in winter, it has proved useful for landscaping and conservation plantings. Unfortunately, Amur maple can escape from cultivation and become a weed, so plantings should be closely monitored. Less cold-tolerant, but more refined in its habits, is the beautiful Japanese maple. This elegant little tree, with its deeply lobed, star-shaped leaves and striking fall color, is a popular ornamental wherever it can be grown. It has been cultivated in its native Japan for centuries, and a great many cultivars are available. Consult your local garden center for its suitability in your area. Many other small maples are native in eastern Asia. Most are very attractive trees, with excellent fall color and in some cases attractive bark, giving them year-round appeal. Not all are adapted to Iowa’s harsh continental climate, but some have shown promise in trial plantings. For more information on these, see “Promising Trees for Iowa” on pages 379 to 381.

Buckeyes and Horsechestnuts, Aesculus L. Ohio Buckeye, A. glabra Willd. Common Horsechestnut, A. hippocastanum L. The genus Aesculus comprises about two dozen species of trees and shrubs, found in temperate areas through much of the northern hemisphere. Species native in North America are usually called buckeyes, while those from Europe and Asia are called horsechestnuts. As a group they are easily identified by their distinctive leaf and fruit, although species differ considerably in size and flower color. Most can be grown far beyond their natural ranges. One species of this genus is native in Iowa, and another is sometimes planted. For information on others that may be useful for landscaping here, see “Promising Trees for Iowa” on pages 379 to 381. Ohio buckeye is the state tree of Ohio; though not well known in other states, it is native throughout most of the Midwest. It is named for its large, nutlike seed, whose smooth brown coat and large pale hilum suggest a buck’s eye. The seed also resembles the chestnut, even down to its starchy interior, but is not edible. It is enclosed in a dry, leathery husk that turns from yellow to brown as the season progresses, splitting open and releasing the seed in fall. There is usually one seed per husk, but some husks may contain two or even three.

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The flowers of Ohio buckeye are less conspicuous than those of some other springflowering trees, but when viewed up close they are quite attractive.

In Iowa, buckeye is native in wooded river valleys across much of the southern and central parts of the state, usually on moist slopes or floodplains but occasionally in dry uplands. It grows quite well in northern Iowa when planted, however, and is used for landscaping throughout the state. Its unusually shaped leaves are among the first to appear in spring, then turn yellow or orange in autumn. Trees grow at a moderate rate, and when planted in the open, they develop low, rounded crowns 25 to 40 feet tall. Disease and insect problems are limited and usually not serious, but individual trees may lose their leaves early because of leaf blotch or leaf scorch. The wood of Ohio buckeye is light, soft, straight-grained, fine-textured, and very pale. It has been used for artificial limbs because it resists splitting and is so light in weight and for food containers because it does not impart a taste or odor. Burls from the buckeye are prized for hand-crafted items such as furniture, bowls, and pens.

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Common horsechestnut is native to the mountains of the Balkan Peninsula but has been widely planted outside this range. It has been cultivated in western Europe since the sixteenth century and was introduced to America in colonial times. It is one of the largest trees with ornamental flowers, attaining a height of 50 to 75 feet and sometimes more. Longfellow’s famous poem about the village blacksmith, who worked beneath a “spreading chestnut tree,” concerned a fine specimen of this species in Cambridge, Massachusetts. Useful attributes of the horsechestnut are its showy white flowers, which occur in large, upright clusters up to one foot long; its interesting dark green leaves; and its adaptability to varied sites. Unfortunately, it has little autumn color and can defoliate prematurely from leaf blotch (a fungus disease) and leaf scorch (a physiological problem often related to hot, dry weather in late summer). Neither condition is fatal, but both reduce the shade and ornamental value of the tree. The seeds are reputedly poisonous. The wood of the horsechestnut is light, soft, brittle, and not naturally durable, but it is even-textured and easy to work. In Europe it is used for food containers, kitchen utensils, artificial limbs, brushes, toys, and small turned articles.

Tree-of-heaven, Ailanthus altissima (Mill.) Swingle This tree from eastern Asia has become a fixture in the southern half of Iowa, escaping from cultivation to neglected areas of towns and cities. Once loose it usually thrives, as it tolerates urban and roadside conditions better than most trees. Tree-of-heaven is not without value, but its vices far outnumber its virtues, and we do not recommend it for planting in Iowa. Its growth is rapid but its wood weak and brittle. Its foliage, though attractive, has a strong odor when bruised and no autumn color. The red seeds of female trees add color for a time but later turn brown and spread the tree everywhere. Its roots sucker profusely, turning one tree into many. Tree-of-heaven, then, is hardly the angel its name suggests. In fact, its name probably originated in reference to its fast growth and large size in its native haunts, where it may reach a height of 90 to 100 feet. In the United States it is usually only 40 to 60 feet tall. Its botanical name means “tallest of the trees-ofheaven,” indicating its large size in comparison to related species.

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Alders, Alnus B. Ehrh. Speckled Alder, A. rugosa (Du Roi) Sprengel European Black Alder, A. glutinosa (L.) Gaertn. The alders are a wide-ranging genus of shrubs and trees, closely related to the birches and important ecologically in cool areas of the northern hemisphere. Like the legumes, they improve the soil by hosting nitrogen-fixing micro­ organisms in nodules on their roots. Though not very important in Iowa, one species is native here and another is planted. Speckled alder is a tall shrub that is common in northern Minnesota, the Great Lakes region, and eastern Canada. It barely ranges into northeastern Iowa, occurring here and there in low, sandy woods and wet areas. The European black alder is a medium-size tree with handsome dark green leaves, of conservation interest because of its value for erosion control and the reclamation of strip-mined land. It was introduced to the United States in colonial times and has since naturalized throughout the Northeast, becoming weedy in some places. Cut-leaf and columnar forms are available for landscaping.

Serviceberries (Juneberries), Amelanchier Med. Downy Serviceberry, A. arborea (Michx.) Fern. Allegheny Serviceberry, A. laevis Wieg. Inland Serviceberry, A. interior Nielsen Round-leaf Serviceberry, A. sanguinea (Pursh) DC Low Serviceberry, A. humilis (A. spicata) Wieg. Saskatoon, A. alnifolia Nutt. The serviceberries are the first of our woodland trees to bloom each spring and among the most useful of our native trees for landscaping. Their April flowers are quickly replaced by tiny apple-like fruits, which attract songbirds when they ripen in late June or early July. In autumn their leaves turn a handsome orange or red. Like the redbud and most other spring-flowering trees, serviceberries are naturally small. The largest grow no more than 35 feet tall, and the smallest are shrubs. Even the tree species are usually multiple-stemmed. In cultiva-

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Serviceberries can be very colorful in fall.

tion their trunks form a round-topped crown, but on the wooded ridges and slopes where they naturally grow, they often take on a crooked, picturesque appearance. The fruits of serviceberries are small, seedy, and only slightly sweet, but they provide a welcome snack after a hike through the woods on a warm summer day. The fruits also make good jams and jellies, but you will have to compete with the wildlife if you try to gather them. The species of serviceberry are not numerous, but the genus is challenging botanically. Identification is complicated by hybridization between species and the short longevity of the flowers, which are important diagnostically. Depending on how the species are defined, five or six are native to Iowa. Downy serviceberry is our most widely distributed species, growing in woods throughout eastern, southern, and central Iowa. Allegheny serviceberry, which is native to northeastern Iowa only, is very similar. Both are trees. Hybrids between the two have been introduced for landscaping. Other native species are distributed as follows: inland serviceberry grows

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298 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s in northeastern Iowa; the low serviceberry is native in the northeastern and north central parts of the state; the round-leaf serviceberry is rare in northern, central, and east central Iowa; and the saskatoon is rare in northwest and north central Iowa. For the distinguishing characteristics of native serviceberries, see the key on page 29.

Pawpaw, Asimina triloba (L.) Dunal Pawpaw is one of our rarest and most unusual native trees. It is found in only a few counties in eastern and southwestern Iowa, where it forms thickets in wooded ravines and along streams. In eastern Iowa, it is said that soldiers returning from the Civil War tossed pawpaw seeds from train windows, accounting for the presence of this species quite far north along the Mississippi River. With its huge, tropical-looking leaves, pawpaw is certainly easy to spot in the woods. It is a small tree, usually no more than 20 to 30 feet tall with trunks only a few inches in diameter. Its odd purple flowers, which are relatively large for a tree, also stand out when they bloom in spring. Pawpaw fruits are peculiar, too — heavy, irregularly shaped, and several inches long, with large seeds and thick yellow or orange flesh. The skin changes from green to greenish yellow as the fruit ripens in autumn, then gradually turns black. Though not the most attractive of fruits, pawpaw has a distinctive flavor that is appreciated by opossums, raccoons, foxes, and many people. Pawpaw is easy to grow from seed and occasionally cultivated. Though best suited to moist, partially shaded sites, it will also grow in the sun. Established trees spread by suckering, so pawpaw should be planted where this won’t be a problem or can be checked by mowing.

Birches, Betula L. River Birch, B. nigra L. Paper Birch, B. papyrifera Marsh. Yellow Birch, B. alleghaniensis Britton (B. lutea Michx.) Dwarf Birch, B. pumila L. European White Birch, B. pendula Roth Asian White Birch, B. platyphylla Sukaczev

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The birches are a larger and more diverse group than many people realize. Their bark comes in a whole palette of colors — not just white — and their leaves are varied too. What ties them together — making a birch a birch —  are their tiny flowers and fruits. Birch flowers are arranged in clusters resembling a cat’s tail, called catkins. The male catkins begin to develop almost a year before they bloom and are visible on the twigs all winter. In spring they open and elongate, release their pollen, then fall to the ground. The shorter female catkins emerge from overwintering buds; after their flowers are pollinated, they gradually change from green to brown. Eventually they disintegrate, releasing their tiny winged, single-seeded fruits. Almost all birches have striking bark. In some cases this changes quite markedly as the trees grow, so that one might not recognize a sapling and a mature tree as the same species. This colorful bark makes birches attractive throughout the year, a most welcome trait in places like Iowa where winters are long. When paired with conifers, they make a beautiful cold-weather scene. Unfortunately, many birches are susceptible to the bronze birch borer and thus short-lived in cultivation. By feeding on the trees’ inner bark, this insect kills the branches and eventually the trunks. Damage usually begins in the upper crown and progresses downward. Infested trees are eventually killed or so badly disfigured that their ornamental value is destroyed. Use of resistant species or cultivars is the best defense, but established trees can be protected with preventive sprays. Contact your local extension office for current recommendations on chemical control. Stressed trees are especially subject to the borer’s attack. Unfortunately, people often create this stress by planting the trees in unfavorable locations. Compare the cool forests where birches grow naturally with the sites where we usually plant them — suburban yards with disturbed clayey soils, surrounded by lawn and exposed to the hot summer sun. Is it any wonder that the trees do not live long? One species that does thrive in Iowa is the river birch, which is native in the eastern and southern parts of the state. Unlike most birches, this is a river bottom tree, adapted to the disturbance that such habitats usually bring, and thus more amenable to human-altered environments. It is also the most southernranging of the birches and thus tolerates the hot, dry weather that Iowa summers bring. Not surprisingly, it is the most borer-resistant of our birches. The bark of river birch changes quite dramatically as the trees grow. It is

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300 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s most attractive when the trees are young, with peeling, salmon-colored flakes often mixed with white. As the trees grow the bark gradually darkens, first turning light orange-brown and later gray. When the trees mature, the trunks resemble black cherry more than they do a birch! In cultivation, river birch develops an oval to pyramidal crown and grows 40 to 70 feet tall. The ornamental effect of its bark is enhanced by planting multiple-stemmed trees and removing the lower branches as the trees grow. Chlorosis (leaf yellowing) is sometimes a problem, caused by either drought or alkaline soil. ‘Heritage’ is a popular cultivar. River birch is very common along some eastern Iowa rivers, particularly the Mississippi and the Wapsipinicon. Its seeds mature in May or early June, long before those of other birches. They need a moist, bare, mineral soil for germination, so early ripening allows them to colonize deposits of silt and sand left by receding spring floods. When the word “birch” is mentioned, many people immediately think of the paper birch, one of the most characteristic trees of the North Woods. Like several other northern trees, its range extends into the northeastern corner of Iowa. The cool, moist climate and thin, well-drained soils there provide the environment it requires, and its gleaming white trunks are a familiar sight on hilltops and wooded slopes. An outlying population occurs along the Iowa River in Hardin County. (See the discussion below.) Paper birch is widely known and admired for its beautiful bark. Birch bark’s strength, light weight, and ability to repel water were greatly appreciated by Native Americans, who used it for making containers and the famous birch bark canoe. The bark is also prized because it can be used to start a campfire during wet weather (though peeling the bark from living trees can injure them). Paper birch is susceptible to borers, so if it is used for landscaping, proper siting is very important. A moist, well-drained soil is best, in a location where buildings or other trees provide protection from afternoon sun. Mulching with wood chips is also advisable. Even with such measures, however, it is likely that borers will eventually find and attack the tree. A third native birch is relatively rare and not well known. Yellow birch is found in just a few northern counties, where it is restricted to steep, usually north-facing bluffs and slopes bordering streams. Even where it is most common, such as Pikes Peak State Park near McGregor, it is scattered in the forest, occupying only a minor part of the canopy.

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Most people know the paper birch, with its gleaming white bark.

If you don’t know the yellow birch, you might not recognize it as a birch. Its bark is not as colorful as other species, ranging from a subdued yellow-gold to light gray. Smooth and tight-fitting at first, it soon becomes scaly or curls into distinctive rolled strips. The tree’s inner bark contains oil of wintergreen, once widely used to flavor patent medicines and still used in candy. You can easily identify the tree at all times of the year by chewing a twig. As with the paper birch and white pine, there is an isolated population of yellow birch along the Iowa River in Hardin County. The origin of these birches and pines, the southwesternmost in Iowa, has long intrigued Iowa botanists. Studies of pollen grains buried in peat bogs have shown that northern trees were widely distributed in Iowa at the end of the last ice age, an indication that the climate then was much different than it is today. The birches and pines along the Iowa River are believed to be relics of these postglacial forests, surviving there only because the environment is especially cool and moist. This section of the Iowa River bordered the glacier, and the area must have been especially scenic in summer, with these attractive trees on their high bluffs, overlooking the ice and the fast-flowing river. For landscaping purposes, yellow birch is subject to the same limitations as paper birch. It is, nevertheless, a very handsome tree with rich, bright yellow

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302 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s autumn color and could be used for trial plantings in cool, moist, protected sites. Yellow birch is a valuable timber tree where it is more common in the northeastern United States and adjacent Canada. Its wood is hard, heavy, strong, and shock-resistant, useful for furniture, cabinets, and other products. The wood of paper birch is similar but somewhat lighter, softer, and weaker. It is used for pulp, toothpicks, tongue depressors, toys, and small turned articles such as spools and handles. It is also an excellent firewood. Our final native birch is only a shrub. Dwarf birch ranges across most of northern North America, but in Iowa it grows only in a few northeastern and north central counties, where it inhabits fens, sedge meadows, and moist prairies. Several exotic birches are planted in Iowa, including the European and Asian white birches. Unfortunately, most of these are susceptible to the bronze birch borer. The cultivar ‘Whitespire’ has shown resistance to the borer and is probably the best choice where a white-barked tree is desired.

American Hornbeam, Carpinus caroliniana Walt. This attractive little tree has a confusing abundance of common names. Hornbeam, musclewood, ironwood, bluebeech — all refer to this single species. Botanists know it by its ancient Latin name, Carpinus. Most of the hornbeam’s English names refer to its hard, heavy, peculiarly twisted wood. This gives its smooth-barked trunks a characteristic musclebound appearance, a useful aid in recognizing a species that is otherwise little different from several other, more common trees. The wood is occasionally used for homemade mallets, levers, tool handles, and other specialty items, but the hornbeam is too small to be important commercially. It does make an excellent firewood, although it seems a shame to cut it for such a mundane purpose when oak, ash, and other equally suitable woods are plentiful. Hornbeam is seldom over 30 feet tall or a foot in diameter. Most Iowa trees are smaller. Like its close relative, the ironwood, it tolerates shade and is usually found beneath a canopy of other trees. The two species sometimes grow side by side, but hornbeam prefers a moister site such as a terrace or lower north-facing slope. Hornbeam is desirable for landscaping and could be more widely planted in eastern and central Iowa. Trees do best when placed in a moist, sheltered loca-

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American hornbeam (right) and ironwood are two small trees of the woodland understory. While their foliage is similar, they can be easily distinguished by bark.

tion where the soil is fertile and slightly acid in reaction. The ornamental value of its twisted trunks is enhanced by encouraging its natural tendency to form clumps. The leaves turn a handsome reddish orange in autumn if the tree is growing on a favorable site. Other species of hornbeam grow in Europe and Asia, and they too are attractive trees. A common European species, C. betulus L., is sometimes planted.

Hickories, Carya Nutt. Shagbark Hickory, C. ovata (Mill.) K. Koch Shellbark Hickory, C. laciniosa (Michx. f.) Loud. Bitternut Hickory, C. cordiformis (Wangenh.) K. Koch Mockernut Hickory, C. tomentosa Nutt. Pecan, C. illinoensis (Wangenh.) K. Koch

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304 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s If any group of trees is distinctively American, it is the hickories. Eleven species are native to the United States, but there are none in Europe and only four in tree-rich eastern Asia. Wherever you go in the eastern United States, you will find at least one kind of hickory, and chances are good that it will be a common and important tree. Hickories are appreciated for both their nuts and their wood. One species, the pecan, is grown as a nut crop in the southeastern United States. Hickory wood is hard, heavy, strong, and shock-resistant, making it useful for the handles of striking tools and a variety of sporting goods. With its interesting grain ranging in color from light yellow to brown to black, hickory is an increasingly popular choice for cabinets and occasionally used for colorful hardwood floors. Because of its high heat content, hickory is also valued for firewood and charcoal. Sawdust and chips from green hickory have long been prized for smoking meats. Iowa’s most common and familiar hickory is also the most aptly named —  the shagbark. It is easily identified throughout the year by its distinctive bark, which separates into large, irregularly shaped strips that curve up at one or both ends, giving the trunk a rough, shaggy appearance. The bark is tough and hard like the wood of the tree, and the pioneers are said to have used it for making boxes. The nuts of the shagbark hickory have an excellent flavor but, like those of many other hickories, are difficult to crack open. They are appreciated by squirrels, chipmunks, raccoons, turkeys, grosbeaks, woodpeckers, blue jays, nuthatches, and many other kinds of wildlife. One can often find young shagbarks in pastures and other uncultivated areas bordering woods, a sure sign that the squirrels did not recover all the nuts they stashed in previous autumns. Shagbark occurs on a variety of sites but is most commonly found in upland woods with white, bur, red, and black oaks. Because of its useful wood and value to wildlife, it is desirable for reforestation and woodlot improvement in Iowa. When given ample room, shagbark grows 70 to 80 feet tall with an open, oblong crown. It is a picturesque, long-lived tree and could be more widely used for landscaping. Unfortunately it can be difficult to transplant and grows rather slowly, so patience is required when planting it. Cultivars are available for those who enjoy its nuts.

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Shagbark hickory is named for its distinctive shaggy bark, which makes it easy to identify at all times of the year.

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306 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s Shagbark has a close look-alike in the shellbark hickory, which is native to the southeastern and south central parts of Iowa. Shellbark is a tree of the lowlands, and like other trees in this habitat, it has suffered from the clearing of bottomland forests. A good place to see it is along the Chariton River downstream from Lake Rathbun. Our most wide-ranging hickory, and the only species in far northwestern Iowa, is the bitternut. It is easily distinguished from shagbark by its bright yellow buds and, when those are out of reach, by its smooth to shallowly fissured bark and slender branches. As its name suggests, its nuts are not known for their palatability. Bitternut can be found on both wet and dry sites but prefers a moist, welldrained soil. It is usually found on stream terraces, the back portions of floodplains, and sheltered slopes with hard maples, basswood, red oak, ashes, and elms. Pathologists are investigating a new disease, caused by a canker associated with attacks by bark beetles, which has killed trees in Iowa, Minnesota, Wisconsin, and other states. Bitternut is a handsome tree, and though it is rarely used for landscaping, existing specimens are worth preserving when wooded sites are developed. It grows faster than most other hickories and, with its bright yellow foliage, stands out in autumn. Two other native hickories are found in southeastern Iowa. The mockernut grows in dry upland woods with oaks and shagbark hickory. The pecan grows in the Mississippi River bottoms as far north as Jackson County. Pecan, of course, is well known for its delicious and thin-shelled nuts. The nuts of mockernut are edible, too, but their shells are thick and hard to open. Its name has been attributed to the fact that its nut meats are much smaller than one would expect from the size of the nut and hardly worth the effort to extract them. Pecan is a southern tree, and people are often surprised to learn that it also grows wild in Iowa. It is sometimes suggested that our Iowa pecans were planted by Native Americans and are thus not truly native. This is a more likely explanation for trees found in Kossuth County than for those along the Mississippi. Our northern trees appear to be a distinct ecotype, differing from southern pecans in that they mature their fruit in our shorter growing season. Pecan is the largest and fastest-growing of the hickories, often attaining a height of more than 100 feet and a trunk diameter of 2 to 4 feet. Its wood is used for furniture, flooring, and cabinetry.

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Northern Catalpa, Catalpa speciosa Warder This tropical-looking tree seems strangely out of place in the prairie towns and farms of Iowa. When Europeans first ventured into the interior of America, the catalpa had a small range centered in the boot-heel region of Missouri. People soon found it to be a hardy and useful species that would grow well throughout the Midwest. Catalpa is seldom planted today, but many fine old specimens remain to remind us of the popularity it once enjoyed. It is one of our largest ornamental flowering trees, attaining a height of 30 to 60 feet with an open, irregularly pyramidal or oval crown. While it is beautiful in bloom, it is not very attractive after its flowers fade and has little autumn color. Catalpa is also a messy tree, littering the ground with its large, coarse leaves and long, pencil-shaped pods. The pods, or Indian beans as they are sometimes called, appear on the branches in midsummer. They change from green to brown when they ripen in autumn, then split open and release the seeds. At least some of the pods remain on the branches throughout the winter, making the catalpa easy to recognize then. The seeds, which have a papery wing resembling a propeller, are easily blown about by the wind. In this way the catalpa sometimes escapes to stream banks, roadsides, open woods, and other uncultivated places. The wood of the catalpa is light, soft, and weak but naturally durable when properly seasoned. Many groves of this species were planted during the 1930s as it thrives in a variety of soils, tolerates droughty conditions, and was reputed to produce good-quality fence posts in a shorter period of time than any other tree. It is still used for fence posts and rails and also for general construction, cabinets, picture frames, and other items. The southern catalpa (C. bignonioides Walt.) is occasionally planted where hardy in Iowa. It differs from northern catalpa in having slenderer pods and smaller flowers that are densely purple-spotted.

Hackberry, Celtis occidentalis L. Hackberry is less well known than it should be, given its abundance in Iowa. Whatever the reason for this, it is certainly not due to a lack of distinctive features. No other tree has leaves quite like the hackberry, and its rough, warty bark, which is usually conspicuous even on saplings, is also unique. Few trees can be so easily recognized at all times of the year.

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308 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s Hackberry has many desirable features as a yard and street tree. It grows moderately fast, adapts to many soil types, withstands drought and temperature extremes, and develops a vase-shaped or rounded crown that casts good shade. It is usually a moderately large tree, 50 to 70 feet tall, but can grow to 100 feet with a trunk 4 feet in diameter. One of its few drawbacks is that its leaves are not especially colorful in autumn, usually turning light yellow. Hackberry has no serious diseases or insect enemies but is susceptible to several minor pests whose damage is mostly aesthetic. Witches’ brooms and nipple galls are especially common. Witches’ broom is a broomlike proliferation of short, stubby twigs, produced by a tiny gall mite and powdery mildew fungus. Nipple galls are small, nipple-shaped outgrowths from the leaves, caused by a tiny flying insect called the hackberry psyllid, which lays its eggs on the developing leaves in spring. The psyllids sometimes become annoying to people in the fall, “biting” skin and invading homes. Hackberry can be found in a variety of habitats, but it is primarily a tree of moist, low-lying woods. Its resistance to wind and its ability to grow well in poorly drained soils recommend it for windbreaks and conservation plantings on sites too wet for conifers. The fruit of the hackberry is a small, hard, one-seeded pit surrounded by a thin flesh that tastes something like a prune or a date. Hackberries are eaten

Nipple galls, which are caused by small insects, are a common feature of hackberry leaves. Though unattractive, they do not seriously harm the tree.

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by many small birds including robins, flickers, cardinals, cedar waxwings, and brown thrashers. They are especially valuable as a wildlife food because they persist on the twigs into winter, long after other foods have become scarce. The pits pass unharmed through the digestive tracts of birds, which explains the prevalence of young hackberry trees in woods, fencerows, and other uncultivated areas. The wood of hackberry is flexible, shock-resistant, and moderately strong, hard, and heavy. It resembles elm but typically has wider sapwood and distinctive yellow streaks. It has been used for furniture, veneer, millwork, sporting goods, boxes and crates, and other items.

Buttonbush, Cephalanthus occidentalis L. Buttonbush is native in wetlands and along shores throughout much of Iowa but common only in the east and south. It grows to be a substantial shrub or small tree with stout stems and a rounded to irregular crown. Though not much planted, it is useful for naturalistic landscaping in poorly drained soils, with handsome, glossy leaves and balls of white flowers in summer. It is adapted to both sun and shade but is more compact and attractive in sun.

Redbud, Cercis canadensis L. It is the destiny of some trees to remain forever small, to never produce the valuable wood or abundant shade of their larger relatives. Nature is full of peculiar ironies, though, and it seems entirely appropriate that the most beautiful flowers are found on the most modest trees. The redbud is one of our best examples. Redbud has many virtues as an ornamental tree and is cultivated over much of Iowa. In form it is irregular and picturesque, making it useful for naturalistic landscapes. Its flowers are relatively long-lived, it tolerates a variety of soils, and it grows well in both sun and partial shade. Diseases and insects are usually not much of a problem. When growing redbud, one does need to be careful about source, especially in northern Iowa. The species grows naturally over most of the eastern United States, and trees from the southern part of the range cannot tolerate our Iowa winters. Here it is best to plant native trees or cold-hardy types such as ‘Columbus Strain.’

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310 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s Native redbuds are found along rivers and streams in southern and parts of central Iowa. Their typical habitat is the understory or edges of established woods, where their small size is actually advantageous. Trees can attain a height of 30 feet with trunks a foot in diameter but are usually much smaller.

Dogwoods, Cornus L. Alternate-leaf Dogwood, C. alternifolia L. Gray Dogwood, C. foemina Mill. ssp. racemosa (Lam.) J.S. Wilson Roughleaf Dogwood, C. drummondii Meyer Red-osier Dogwood, C. stolonifera Michx. (C. sericea L.) Silky Dogwood, C. amomum Mill. ssp. obliqua (Raf.) J.S. Wilson Roundleaf Dogwood, C. rugosa Lam. Flowering Dogwood, C. florida L. Kousa Dogwood, C. kousa Hance. Cornelian-Cherry Dogwood, C. mas L. Most dogwoods are shrubs, but they are common enough and grow tall enough to be included in a book about trees. Six species are native in Iowa, and several others are planted. Dogwoods are distinctive as a group, but the species are very similar to one another and often difficult to identify. Characteristics used to separate species include the shape of the leaves, the type and relative abundance of hairs on the leaves, the color of the twigs and pith, the arrangement of the flowers and fruits, and the color of the fruits. For help in identifying them, see the key on page 31. Whatever their species, dogwoods are important to wildlife. Their small, berrylike fruits are eagerly devoured by many songbirds and game birds, including robins, bluebirds, thrushes, waxwings, catbirds, pheasants, quail, and turkeys. Dogwood thickets provide shelter and nesting cover for small birds and mammals, while the foliage and stems provide browse to deer and rabbits. Dogwoods are also very useful for landscaping. Adaptable, hardy, and easy to grow, they provide attractive flowers, handsome foliage, good red or purple fall color, brightly colored fruits, and, in one species, bright red winter stems. Our most distinctive species is the alternate-leaf dogwood, which is native in moist upland woods as far west as the Des Moines River. As its name suggests, this is our only dogwood with alternate leaves. It is also one of our largest dogwoods, frequently becoming treelike in stature and 10 to 25 feet

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tall. Many people call it the pagoda dogwood because its numerous horizontal branches are arranged in tiers like the stories of a pagoda. This feature and its attractive flowers and foliage make it useful for landscaping. Gray dogwood grows in dry open woods and edges throughout all but the northwestern corner of Iowa, often forming thickets. It is easily recognized by its open, panicle-like flower clusters, which are about as tall as wide and have bright red branches. Its ripe fruits are white. Roughleaf dogwood is similar but grows larger — 10 to 15 feet tall — with a more compact, flat- or round-topped cluster of flowers and fruits. It is native in thickets, open woods, and wood edges across most of Iowa, though more common in the south than the north. In nature one can sometimes find plants that are intermediate between this and the previous species and are presumably hybrids between them. Red-osier dogwood is easily recognized by its bright red stems. It is native in moist, low-lying places in northern Iowa, but it is seen more frequently in cultivation than in the wild. Silky dogwood grows along stream banks, shorelines, and edges of bottomland woods throughout most of the state but is common only in the northeast. It resembles gray dogwood but has flat-topped flower clusters with greenish branches and blue fruits. Roundleaf dogwood is native on moist, wooded slopes in the eastern onehalf to two-thirds of Iowa, though common only in the northeastern corner. It is one of the easiest dogwoods to identify, having roundish leaves and greenish stems usually blotched with purple. In addition to these shrubby natives, several small-tree dogwoods are planted in Iowa. The best known of these is the flowering dogwood, beloved in the eastern United States for its beautiful spring flowers. Unfortunately, this handsome tree is susceptible to dogwood anthracnose, a deadly disease that is spreading throughout its natural range. If planted in Iowa — which is not recommended because of the disease — flowering dogwood should be obtained only from a northern source, as trees from the South are not flower-bud hardy in winter. A small tree with similar flowers, though blooming later, is the kousa dogwood from eastern Asia. It is reportedly resistant to anthracnose and is be­ing planted as a replacement for the flowering dogwood. In an appropriate location — a moist, fertile site protected from winter winds — this could be tried in southern and eastern Iowa.

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312 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s The Cornelian-cherry, a dogwood from Europe, is hardy in the eastern, southern, and central parts of Iowa. Its small yellow flowers appear early, usually in April, a most welcome sight after a long, cold winter. The tart but edible fruits that follow are bright red when ripe and about 5/8 inch long. Corneliancherry develops a rounded crown about 20 to 25 feet tall.

Hazels, Corylus L. American Hazel, C. americana Walt. Beaked Hazel, C. cornuta Marsh. The hazels are a small but important group of trees and shrubs, widely distributed in temperate regions of the northern hemisphere. Their tasty nuts, called hazelnuts or filberts, are grown commercially in Europe, southwest Asia, and the Pacific Northwest. The two species native to Iowa are shrubs. American hazel grows in or near woods throughout much of the state but is much less common today than it was in presettlement times, when it formed large thickets along the prairieforest border. Beaked hazel, named for the elongated neck of its nut-husk, grows on cool, wooded slopes in northeast Iowa. American hazel is adaptable and easy to grow, useful for shrub borders and conservation plantings. Squirrels and chipmunks relish the nuts, grouse eat the buds and catkins, and songbirds nest among the branches. The hazel’s handsome leaves turn yellow, orange, and purple in autumn. Hazels are among the first shrubs to bloom in spring. The male flowers occur in long catkins that drop soon after shedding their pollen. The female flowers are mostly hidden within the overwintering buds but sport beautiful bright red stigmas.

Hawthorns, Crataegus L. Downy Hawthorn or Red Haw, C. mollis (T. & G.) Scheele Cockspur Hawthorn, C. crus-galli L. Dotted Hawthorn, C. punctata Jacq. Margaret’s Hawthorn, C. margaretta Ashe Washington Hawthorn, C. phaenopyrum (L. f.) Med. Fleshy Hawthorn, C. succulenta Shrad.

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Pear Hawthorn, C. calpodendron (Ehrh.) Med. Fireberry Hawthorn, C. chrysocarpa Ashe Scarlet Hawthorn, C. coccinea L. (C. pedicellata Sarg.) Frosted Hawthorn, C. pruinosa (Wendl.) K. Koch Spreading Hawthorn, C. disperma Ashe Few tasks are more difficult than sorting out the many kinds of hawthorns that grow wild in North America. Hybridization and the existence of many local variants make their taxonomy very difficult. Most people — even many naturalists — are content to call them hawthorns and leave it at that! Though diverse in foliage and form, hawthorns are much alike ecologically. All are small trees with a penchant for well-lighted places. Common habitats are clearings, fencerows, the edges of woods, and pastures near woods. Most species will grow in a variety of soils, and some are found in both bottomlands and uplands. The small, apple-like fruits of hawthorns are called haws or thorn apples. They vary in size, color, and shape from one species to another but are usually round, 1/4 to 1/2 inch in diameter, and red when ripe. They also vary considerably in texture and taste. Each haw contains one to five bony seeds or nutlets that make up the bulk of the fruit. Haws are eaten by many kinds of wildlife including pheasants, grouse, songbirds, raccoons, skunks, and squirrels. Most hawthorns are thorny — often wickedly so — and for this reason they are not much used for landscaping. They can be picturesque in form, however, and where nice specimens are growing in parks and newly developed areas, they are worth keeping. To their credit, hawthorns produce attractive flowers and fruits, grow well in difficult sites, and often color well in autumn. Their main limitation, besides their thorns, is their numerous disease and insect problems. None of these is really harmful, but they can seriously mar a tree’s appearance, especially later in the growing season. Leaf rust, which spreads from eastern redcedar and other junipers, is especially troublesome for some species. Our most common species is the downy hawthorn, which ranges throughout all but the extreme northwestern corner of Iowa. It is also the largest, growing 35 to 40 feet tall, and one of the easiest to identify, with large, prominently lobed leaves widest near the base. Its crown is broad and rounded, with wide-spreading ashy gray branches that are sometimes nearly thornless. The showy white flowers appear in early to mid May, early for a hawthorn. The

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Cockspur hawthorn is admired for its dark green, glossy leaves. Its fruits can be attractive too but are sometimes infected with an unsightly rust disease.

haws, which are sweet and edible, are attractive when they ripen in August and September. If not defoliated early by rust, the leaves turn yellow or orange in autumn. The distinctive cockspur hawthorn is native across the southern half of Iowa though not common in the west. It is readily identified by its narrow, unlobed, glossy leaves and unusually long thorns. A small tree up to 25 feet high, cockspur develops a low, rounded crown of wide-spreading branches. Because it is such a handsome tree, its thornless variety inermis is sometimes planted. The fruits persist on the branches in winter, providing food for birds. Dotted hawthorn and Margaret’s hawthorn grow 20 to 25 feet tall, with leaves shallowly lobed on their upper half. The former is a flat-topped tree with long, horizontal branches, native throughout most of the state. Margaret’s hawthorn, native across the eastern half of Iowa, has a narrow, open crown. A fifth hawthorn that Iowans are likely to see, though only in cultivation, is the Washington hawthorn. Its upright branching gives it a narrower crown than most hawthorns, and its leaves and fruits are smaller. Its foliage turns orange, red, or purple in autumn, and its small, berrylike haws persist on the trees all

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Washington hawthorn produces small red fruits that persist into winter, providing food for birds.

winter, providing food for birds. It is native to the southeastern United States. Several other hawthorns grow wild in Iowa but are not common here. These are the fleshy and pear hawthorns, rare to uncommon across most of the state; the fireberry hawthorn in northern Iowa; the scarlet hawthorn in eastern and central Iowa; the frosted hawthorn in central and southeastern Iowa; and the spreading hawthorn in counties near the Missouri border. For the characteristics of these species, consult one of the manuals listed in the bibliography. The wood of hawthorns is hard, heavy, and tough. It is occasionally used for tool handles, canes, small turned articles, and fuel, but it is unimportant commercially because the trees are small and usually crooked.

Persimmon, Diospyros virginiana L. Persimmon is a medium-size tree that grows naturally throughout the southeastern United States. It has long been cultivated in southern Iowa and persists around abandoned farmsteads, forming large thickets. Some wild trees might be native, but their origin is uncertain.

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316 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s Persimmon is best known for its fruits, which are sweet and tasty when fully ripe, after their skin wrinkles and their flesh softens in late autumn. Before that they are famously astringent, and no one repeats the mistake of eating them too soon. The fruits are much appreciated by opossums, raccoons, skunks, foxes, and many birds as well as people. Trees are either male or female, so only some bear fruit. Persimmon is also valued for its wood, which is hard, heavy, and strong and wears very smooth. It is used for shuttles, spools, bobbins, golf club heads, and other specialty items. Though not much grown today, persimmon is a handsome tree with dark green leaves, picturesque branching, and dark, blocky bark. If planted it should be placed where one can mow around it or where its suckering nature won’t be a problem.

Russian-olive and Kin Russian-olive, Elaeagnus angustifolia L. Autumn-olive, Elaeagnus umbellata Thunb. Buffalo Berry, Shepherdia argentea Nutt. Most ornamental trees are planted for their showy flowers or fruits, but the Russian-olive is valued for another feature — its handsome foliage. When viewed from a distance, this gives the tree a distinctive silver-gray cast that stands out in the landscape. If the leaves are inspected more closely, the source of this color can be seen — an array of small silvery scales covering the dark green leaves and shoots. When magnified these resemble tiny stars. Russian-olive is a small tree, growing 15 to 20 feet tall with a short trunk and an open, rounded crown. Handsome, hardy, and adaptable, it has been widely planted in Iowa for landscaping, conservation, and highway beauti­ fication. Like the legumes, it improves the soil through nitrogen-fixing bac­ teria in nodules on its roots. Wild birds and mammals eat its small silvery fruits, which persist on the branches in winter. Unfortunately, like most fast-growing trees, Russian-olive is usually shortlived in cultivation. Though well formed when young, it tends to develop a straggly, disheveled appearance as it ages. When stressed by injury, old age, or poor drainage, it may die back from verticillium wilt or canker. Frequent pruning to remove weak branches and stimulate new growth will help keep the tree vigorous and attractive.

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Russian-olive is native from central Asia to southeastern Europe, growing in a wide variety of habitats. Its fruits are used there to make a strong alcoholic beverage, and its bark and foliage are employed in tanning. Its wood is harvested for posts, beams, fuel, and musical instruments. Despite its name, Russian-olive is not related to the olive of commerce. It belongs to the small but widely distributed oleaster family (Elaeagnaceae), easily distinguished from other woody plants by the presence of tiny scales on the leaves and twigs. Shrubby relatives that grow in Iowa are the autumnolive, which was introduced from eastern Asia, and the buffalo berry, which is native in the Loess Hills. Autumn-olive resembles Russian-olive but has juicy red fruits and brown scales in addition to the silvery ones. Buffalo berry differs from both in having opposite leaves. Autumn-olive can escape from cultivation and become invasive, so its planting should be discouraged in Iowa.

Wahoo and Kin, Euonymus Wahoo, E. atropurpureus Jacq. Burning Bush or Winged Euonymus, E. alatus (Thunb.) Sieb. Wahoo is a single-stemmed, treelike shrub growing to about 10 feet tall. It is native throughout Iowa in moist, open woods and low-lying areas near woods, often forming thickets. Its peculiar fruits are similar to those of its close relative, the bittersweet, but differ in being deeply lobed. The colorful seeds are reputedly poisonous. The Sioux used the hard, close-grained wood of this species for arrows, and it is believed that the name wahoo was derived from a Native American word meaning “wood of the arrow.” European American settlers pulverized the bitter root bark and employed it in home remedies. Eurasian relatives of the wahoo are cultivated in Iowa, especially the winged euonymus or burning bush. These can escape and become weeds, so they should be planted with discretion.

Ashes, Fraxinus L. Green Ash, F. pennsylvanica Marsh. White Ash, F. americana L. Black Ash, F. nigra Marsh. Blue Ash, F. quadrangulata Michx.

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318 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s Like the elms half a century ago, ashes are a familiar sight wherever one goes in Iowa. Unfortunately, it appears that they too may disappear as common trees, this time because of a small green beetle, the emerald ash borer. As this book goes to press, Iowans are watching nervously as the borer spreads westward from the Great Lakes area. For updates and more information, see the ISU Extension web site at http://www.extension.iastate.edu. Four species of ash are native in Iowa, and all are threatened by the borer. Green ash is the most common and widely distributed. Attractive, adaptable, and fast-growing, it has been planted almost everywhere — along streets, in parks, near homes, and in farm groves. Striking in autumn with its bright golden leaves, it is a principal source of fall color in many places. It is also easy to recognize, even in winter, with its ashy gray, diamond-patterned bark and stiff, curving branches. Native green ash is usually found in low areas near water, such as floodplain forests and lakeshores. Close observers will notice two distinct forms of the species. The more common type, called variety subintegerrima, has hairless leaves and twigs. Variety pennsylvanica, often called red ash, has densely hairy twigs, and the leaves are usually hairy beneath. Even within these types, there is wide variation in the shape of the leaflets and other features.

The leaves of white and green ash resemble one another in summer, but their fall color is quite different—purple in white ash and yellow in green ash.

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The white ash, another common species, is a tree of upland woods. It, too, is valued as an ornamental, especially in cultivar form. White ash resembles the green ash in leaf, twig, and bark, but its leaflets are more clearly stalked and either entire or not so obviously toothed. It can be easily distinguished in autumn, when its foliage turns purple. The wood of both species is valued for its strength, hardness, straight grain, and resistance to shock, which make it useful for long tool handles, baseball bats, paddles, oars, furniture, flooring, and millwork. Ash is also an excellent firewood (which is hastening the trees’ demise as the emerald ash borer is easily transported in that way). Iowa’s third native ash, the black ash, ranges across the eastern half of the state but is rarely planted and not well known. It grows on floodplains, terraces, ravines, and the bases of steep, sheltered slopes, usually as a minor component of the forest canopy. Associated trees include silver maple, cottonwood, black walnut, and hackberry in bottomlands and hard maple, red oak, and American basswood on higher ground. The wood of black ash is somewhat lighter, softer, and weaker than that of the white and green ashes and is usually marketed separately from those species. Native Americans and pioneers used the wood for making baskets, as it is tough and flexible and splits easily along its narrow growth rings. Our least common species is the blue ash, restricted to dry river bluffs in extreme eastern Iowa. From Iowa its range extends south to Arkansas and east to Tennessee, Kentucky, and Ohio. Blue ash is easily identified by its square twigs, which are often winged. Blue ash has perfect flowers but the other species are dioecious, meaning that the male and female flowers are found on separate trees. Female trees produce prodigious numbers of small, winged seeds, which often persist on the branches in winter. Eventually the seeds are released and dispersed by the wind. In this way, young ash trees may turn up almost anywhere, including hedges, shrubbery, gardens, and fencerows. As in other wind-pollinated trees, ash flowers appear in early spring before the leaves. The male flowers occur in small, tight bunches on the twigs and usually drop after shedding their pollen. From time to time they are infested with a tiny mite, which causes them to develop aberrantly and persist. The resulting brown galls are especially visible in winter after the leaves are gone.

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Ginkgo, Ginkgo biloba L. The ginkgo is a unique and remarkable tree, little changed over millions of years, the last survivor of an ancient family. Everything about it is different, from its unusually shaped leaves to its peculiar flowers and fruits (which, technically speaking, are neither flowers nor fruits). When you next see this living fossil, remember that dinosaurs once gazed upon it too and may have eaten it as well. The ginkgo was once widespread in the northern hemisphere, including parts of North America, but it died out here and almost everywhere else. Fortunately, the species survived in the mountain valleys of China, and from its refuge there, people again distributed it throughout much of the world. Today one can find planted trees in most of the United States, including Iowa. There are many reasons to plant the ginkgo, in addition to its unusual heritage. It is a very handsome tree, with beautiful leaves that turn a bright golden yellow in autumn. As one might guess from its long persistence on earth, it is also a tough and adaptable species, growing in many different soils, resisting

Ginkgo is a handsome and long-lived tree.

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drought once established, and tolerating urban conditions. The ginkgo is also nearly pest-free, having apparently outlasted its disease and insect enemies. It can be long-lived too; there are trees in the Orient reputedly more than 1,000 years old. Though a broadleaf deciduous tree, the ginkgo resembles the conifers in some key features and is considered more closely related to them than it is to other trees. When young it has the pyramidal form so common among conifers, and like them, it lacks pores (vessels) in its wood. Also, as in conifers, the ginkgo’s reproductive structures are not truly flowers. The male and female parts occur on separate trees, appearing at the ends of spur shoots in spring. The male parts are tiny sacs that occur in elongated, catkinlike clusters, dispersing their pollen by wind. The female parts are borne in pairs at the ends of short stalks. Following pollination and fertilization, the female parts develop into seeds resembling plums. Another unusual feature, and unfortunately not a pleasant one, is the foul odor produced by the fleshy outer part of the seed when ripe. For this reason, male cultivars have been developed and are preferred for landscaping. Interestingly, the seed’s inner, nutlike portion is roasted and eaten by Asians, who consider it a delicacy. Raw seeds are reputedly poisonous, and even the cooked seeds may be toxic if eaten in excess. The seeds apparently gave the tree its name. “Ginkgo” is usually attributed to the Chinese words gin-yo or gin-go, meaning “silver apricot.” Ya chio, or “leaf of a duck’s foot,” is another ancient Chinese name. Ginkgo is also called maidenhair tree because its leaves resemble those of the maidenhair ferns. In cultivation the ginkgo usually grows rather slowly. As trees mature they tend to lose the symmetrical form of their youth and become more irregular in shape. They eventually reach a height of 50 to 80 feet.

Honey Locust, Gleditsia triacanthos L. One could be forgiven for assuming that wild and cultivated locusts are different species. The wild ones, with their terrible thorns and long, messy pods, are trees one would never want to plant. Fortunately, nature has given us locusts that bear neither thorns nor fruit, and from these many useful cultivars have been developed. The locust owes its popularity at least in part to the Dutch elm disease, which created a need for new, fast-growing shade trees. Handsome, adaptable,

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The attractive and adaptable honey locust has been widely planted as a shade and street tree in Iowa.

and easy to grow, it produces a light, open shade that is compatible with lawns. It is also resistant to salt, which makes it useful for street and highway plantings. Its compound leaves turn yellow in autumn, and because the leaflets are so small, they create minimal litter when they fall. The cultivars vary in size and habit, with the largest growing up to 75 feet tall. Honey locust was once considered trouble-free, but as it has become more common, so have its pests. Cankers and borers can seriously injure trees, especially those stressed by drought or injury. Mimosa webworm, which creates areas of brown foliage in summer, is a lesser threat but does mar the trees’ appearance. Good cultural practices will minimize the more serious problems. Native locusts were probably uncommon at the time Iowa was settled, growing with other trees along rivers and streams. Agriculture benefited the species by creating open, sunny places for it to grow and providing a convenient way to disperse its seeds. (Cattle eat the pods, which contain a sweet, honeylike pulp, then pass the seeds unharmed.) In many places locusts have become weeds in pastures and fencerows. The attractive reddish wood of the honey locust is hard, heavy, strong,

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durable, and shock-resistant. It is used for general construction, furniture, interior finish, fence posts, and fuel. Resembling the locust in leaf if not in size is the indigo bush, Amorpha fruticosa L. This tall shrub is not well known but is native throughout Iowa along lakeshores, stream banks, and the borders of marshes, particularly in the lakes region in the northwest. It is easily overlooked except in early summer, when its branches are tipped by tight racemes of small purple flowers with bright orange stamens. In winter it can often be identified by a common spindle-shaped twig gall.

Kentucky Coffee Tree, Gymnocladus dioicus (L.) K. Koch Anyone who gardens or studies our native flora knows that plants can have misleading names. The Kentucky coffee tree is a notable example. It is no relation to the coffee of commerce, nor is it confined to the state of Kentucky. It ranges, instead, throughout the Midwest and is a legume like peas and beans. Calling it a locust would not be far from the mark. Coffee tree has huge compound leaves that can span more than a foot in width and two feet in length, the largest of any native tree. Its stout twigs and sparse branching are perhaps a reflection of this, as it must support the weight of its large leaves but doesn’t need as many of them. Today we don’t make coffee from the tree’s seeds, as the settlers in Kentucky are said to have done, but we can use it in other ways. An energy saver near buildings, it provides good shade in summer, and then when its leaves fall, its open crown allows ample sun to pass. It’s a good choice for reforestation, city parks, and street-side plantings too. Though handsome throughout the year, the coffee tree is especially attractive in winter, when its picturesque branching and handsome, scaly bark are more easily appreciated. Its distinctive twigs also merit a closer look. Much stouter than those of other trees, their surface is marked with large, heartshaped scars left by the fallen leaves. When the twigs are cut in two, their thick, bright orange pith is revealed. The large, stout pods of female trees also add interest when the leaves are gone. Coffee tree grows rather slowly when young, then at a more moderate rate. When it has room to spread, it develops a rounded crown 60 or more feet tall. An adaptable species, it tolerates both clay and alkaline soils. Diseases and insects are rarely a problem.

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324 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s No tree is perfect, and the coffee tree does have its limitations. Saplings are not much to look at, with their sparse, stout branches. Larger male trees may produce root suckers, but these are not a problem if the surrounding area is mowed regularly. Some people dislike the pods, which fall intermittently over the winter and must be cleaned up in spring. Native coffee trees can be found here and there across Iowa, most commonly in forested bottomlands, terraces, ravines, and lower slopes. Where they do occur, they can be common or rare. The cause of their erratic distribution is unknown, but human hands may have been partly responsible. Native Americans are said to have eaten the pods and used the seeds in games, and they may have planted trees (or discarded seeds) at their encampments. The hard, heavy, durable wood of the coffee tree resembles that of honey locust. It is used for fence posts, railroad ties, cabinetwork, interior finish, and general construction.

Witch-hazel, Hamamelis virginiana L. The witch-hazel is one of our most peculiar native plants, particularly in its flowers and fruits. Most trees and shrubs bloom in spring, but witch-hazel waits until fall, after most species have lost their leaves. When its small yellow flowers finally appear, they are more often detected by smell rather than sight, filling the air nearby with their strong and distinctive fragrance. They develop the following year into small brown pods, which forcibly eject the shiny black seeds when ripe. Today the witch-hazel’s main use is landscaping, but in the past it was valued for other purposes. An aromatic extract from its bark, twigs, and dried leaves was widely used in after-shave lotions, tonics, and patent medicines. Forked branches were favored for water-witching. Though usually a shrub, witch-hazel can become a small tree up to 25 feet tall. It is native on moist wooded slopes in northeast and extreme east central Iowa.

Black Walnut, Juglans nigra L. Few people need an introduction to the black walnut. Common throughout Iowa, it is well known for both its valuable wood and its edible nuts. It is one of our state’s most characteristic and important trees.

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Black walnut is the favored wood for making gunstocks. It is also prized for furniture and cabinetry.

The beautiful heartwood of the black walnut has long been regarded as the choicest native wood for fine furniture, cabinets, veneer, and gunstocks. Popular for its rich brown color and attractive grain, walnut is also admired for its strength, hardness, durability, resistance to shock and warp, and good machining and finishing qualities. Iowa is a leading producer of this important wood. Less important commercially, but appreciated by many people, are the walnut’s tasty nuts. Though expensive and hard to crack open, these have a distinctive flavor that is valued in baking and flavoring. Members of the Iowa Nut Growers Association are actively selecting and evaluating trees, looking for improved kernel quality and easier cracking, and are a good source of information and propagating materials (http://www.iowahort.org). The shells of the nuts are useful too. Composed of minute cells called sclerids, they are ground to a powder that is used in paints and varnishes, as a dry lubricant, and in other products. To harvest walnuts for personal use, collect them as soon as they fall from the trees. Remove the green husks promptly, using gloves to avoid staining your hands. (An old-fashioned, hand-cranked corn sheller works well for this purpose.) Clean the nuts by soaking them for 30 minutes in a bucket of water and then stirring them. Let them air-dry in a well-ventilated place secure from rodents, for example, in mesh bags in the garage, then store them in a cool place. Opening the nuts is best accomplished with a heavy-duty nutcracker designed for black walnuts. Not surprisingly, black walnut is an excellent choice for reforestation and woodlot improvement in Iowa. Most landowners plant it primarily for timber, but its nuts are another source of income that should not be overlooked. For

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326 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s more information on growing black walnut in Iowa, contact your local extension office or go to http://www.extension.iastate.edu. Despite its value as a forest and orchard tree, black walnut is not much used for landscaping. Its nuts are messy, and a fungus called anthracnose may cause its leaves to drop early. The roots and nut-husks release a substance called juglone, which is antagonistic to some kinds of garden and ornamental plants. If one can overlook these faults, walnut is a strong, stately, and moderately fast-growing shade tree. When its leaves do persist into fall, they often turn a handsome yellow. Native black walnut occurs in a variety of habitats but is most commonly found on the rich, well-drained soils of bottomlands, terraces, and lower slopes. On such sites it often grows 70 to 90 feet tall with a trunk 2 to 3 feet in diameter and sometimes even larger.

Butternut, Juglans cinerea L. Butternut is closely related to black walnut, differing most obviously in its elongated nuts and pale gray bark. It, too, has a beautiful and useful wood, but it is a smaller tree and of less importance commercially. Butternut is native in ravines and stream valleys across most of eastern and central Iowa. Unfortunately, it is becoming scarce because of butternut canker, which produces sunken, black lesions that girdle its trunks and branches, eventually killing the tree. Older Iowans remember a time when butternuts were more common and they enjoyed pleasant walks in the woods to collect the nuts. The light brown heartwood of butternut is straight-grained and easily worked, lighter and softer than black walnut. It is used for furniture, veneer, millwork, and small turned articles. The tree’s sap yields a sweet syrup when boiled down, and the husks of its fruits were once used to dye clothing.

Sweetgum, Liquidambar styraciflua L. Sweetgum is common in river bottom forests of the southeastern United States, ranging north along the Mississippi River valley into southern Illinois. Its handsome, star-shaped leaves turn shades of yellow, red, and purple in late autumn, making it a popular ornamental where the climate is warm. Unfortunately, it is not dependably hardy in most parts of Iowa, and if planted here, it is best to use trees from the northern part of the range only.

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Though not hardy in all parts of Iowa, sweetgum is desirable for its bright autumn color.

Sweetgum is an important timber tree where native. Its moderately hard and heavy wood is used for veneer, furniture, plywood, and pulp.

Tulip Tree, Liriodendron tulipifera L. The beautiful tulip tree is one of the most characteristic trees of the eastern United States. Tall, straight, and fast-growing, it is a common inhabitant of moist upland forests as far west as Michigan, Indiana, and the southern Mississippi River valley. In Iowa it is planted as an ornamental in the southern, eastern, and central parts of the state. Tulip tree is named for its large, tuliplike flowers, which are green with large orange blotches on the inside. These bloom around the first of June, usually on branches high overhead. As the growing season progresses, they become conelike clusters of dry, winged seeds. Tulip tree is a close relative of the magnolias, and a comparison of its flowers to theirs will show many similarities.

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328 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s China has its own species of tulip tree, the only other one in the world. This pattern of distribution — sister species in eastern North America and eastern Asia and no relatives elsewhere — is actually quite common and has fascinated people for years. It is attributed to episodes of changing geology and climate, which fragmented an ancient forest that encircled the northern hemisphere. As time passed, the separated populations of each species evolved into new species. When the glaciers later forced them south, they survived only in eastern North America and eastern Asia, where the north-south-oriented mountains offered no barrier to their migration. Tulip tree is also called yellow poplar and tulip poplar because its wood has similar qualities to that of the poplars. Important where the tulip tree is native, the wood is used for veneer, furniture, plywood, interior finish, pulp, and many other products.

Honeysuckles, Lonicera L. The honeysuckles are a large genus of shrubs and vines, distributed throughout most of the northern hemisphere. Two viny species are native in parts of Iowa, but the shrubby species one commonly sees were imported from Europe and Asia. Unfortunately, the widespread planting of these species has turned out to be a terrible mistake, as they have become invasive in Iowa woodlands. Honeysuckles are a threat to trees, because they compete with seedlings for light and space, and to native wildflowers. Many woodland wildflowers are present for only a short time in early spring, before the trees leaf out, using the abundant light of that season to quickly grow, flower, and fruit. Honeysuckles leaf out much earlier than the trees, intercepting that light when the wildflowers need it most. Wherever honeysuckles take over a woods, wildflowers decline in both abundance and diversity. Honeysuckles were introduced in part because they are beneficial to birds, providing both food and cover. Fortunately, one does not have to give up the birds when removing these shrubs from a landscape. There are many good native shrubs that can be used in their place, including hazels, dogwoods, and viburnums. Because they leaf out later than honeysuckles, these do not threaten spring-blooming plants. Honeysuckles are perhaps best controlled in late fall because they retain their leaves longer than native shrubs and are easily spotted then. If the shrubs are small, they are easily pulled up by hand or grubbed out with a shovel.

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Larger plants should be cut at ground level and their stumps treated with herbicide. (Care should be exercised in using these products, as some can be translocated to the roots of nearby trees.)

Osage Orange, Maclura pomifera (Raf.) Schneid. The fruit of this tree is a most interesting and wonderful thing. Large, bright green, and knobby, it can exceed a grapefruit in size. An orange it’s certainly not, although when fresh it has a similar scent. Hedge apples and monkey brains are other common names. It’s a shame a fruit this large isn’t edible. Break one open, and you’ll find a white gluelike sap inside. Squirrels and quail eat the seeds, but nothing seems to like the pulp, not even the bugs. In fact, people have long used Osage oranges to keep household pests away. According to studies by Joel Coats and his students at Iowa State University, fragments and extracts from the fruits are repellent to cockroaches. Osage orange is native to a small area in the south central United States, but it has been widely planted across southern Iowa and other midwestern states.

Osage orange is often found in rows, reflecting its former popularity as a living fence.

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330 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s An adaptable species, it will grow almost anywhere that isn’t too cold, resisting wind, disease, pests, salt, and drought. Before barbed wire was invented, it was a popular living fence. Later, it was widely used for depression-era conservation programs. Some of those planted trees survive today, and their offspring can be found in woods, pastures, and ravines nearby. If the Osage orange succeeds so well when people plant it, in places so far north of its natural range, why wasn’t it more widely distributed when the settlers arrived? Some scientists think it was more widespread in ages past. According to their hypothesis, a fruit so big must have been eaten by giant animals, which then dispersed the seeds wherever they roamed. If those animals later died out, as many ice-age mammals did, there would be no way for the tree to get around. After the glaciers pushed it south, the Osage orange would have no means to colonize its former range. If you like this tree, you may have noticed the natural variation in its form, the thorniness of its twigs, and the size of its fruits. Also, since individuals are either male or female, some never produce fruits. Because it is so tough, and its foliage so attractive too, it does have potential for urban and highway plantings, even as a shade tree. Horticulturists have made many selections over the years, and the Brenton Arboretum near Dallas Center is now collecting the best of these. The wood of Osage orange is extremely hard, heavy, tough, and durable, and it shrinks or swells very little compared to the wood of other trees. A beautiful golden-yellow or bright orange when first cut, it later turns brown. It is valued for fence posts, insulator pins, and other specialty uses. Native Americans found the gracefully curved branches to be an excellent choice for hunting bows.

Saucer Magnolia, Magnolia ×soulangeana Soul. Most magnolias are trees of warm, southern climates but the saucer magnolia, a hybrid between two Asian species, is hardy across much of Iowa. It is much appreciated for its large, showy flowers, which appear before the leaves in April. They vary from white to deep purple in color, depending on cultivar, but are rose-pink in most of the trees grown in Iowa. Saucer magnolia often grows 20 to 30 feet tall, but its general appearance is more shrublike than treelike. Its trunk usually divides a few inches above the ground, giving way to a broad, rounded crown of numerous upward-curving

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branches. Trees should be grown in an elevated, protected spot, as the flowers are easily destroyed by spring winds and frosts. Several other magnolias are planted in Iowa, including the star magnolia [M. stellata (Sieb. and Zucc.) Maxim.] and the cucumber tree (M. acuminata L.). Star magnolia, a native of Japan, is similar to the saucer magnolia but is a smaller tree whose flowers have narrower and more numerous petals. Cucumber tree, a large forest tree of the eastern United States, has green flowers that appear after its leaves in late spring. In recent years, plant breeders have developed several new cultivars of magnolias, including some with yellowish flowers.

Apples and Crabapples, Malus Mill. Common Apple, M. pumila Mill. Prairie Crabapple, M. ioensis (Wood) Brit. Flowering crabapples, Malus cultivars Mill. In temperate regions such as Iowa, no group of small trees is more diverse or more valued than the genus Malus, the apples and crabapples. Among the hardiest of all our small trees, they are important for both food and landscaping. We call them apples or crabs, depending on the size of the fruits and how we use them, but their basic botanical features are much the same. The most famous member of the genus is, of course, the common apple. This useful tree has been grown in North America for so many years, it’s hard to believe it isn’t native. It must have been one of the first trees introduced from Europe, as it was widely used in colonial times for eating, cooking, and processing into cider. Apples have been grown in Iowa for many years, too, and before the Armistice Day blizzard in 1940, they were a major crop here. Thousands of trees were killed in that storm, and while apples are still grown here commercially, the industry is not what it once was. Ornamental crabs are derived from several wild species, but not so the apples. Most of the varieties we enjoy today are descended from a single, highly variable species that is native to central Asia. There are still fruit forests of apples and other trees in that part of the world today, although they have been greatly reduced by human development. For an interesting account of these wild trees, see The Story of the Apple by B. E. Juniper and D. J. Mabberley. Like the cultivars of other trees, apple varieties are clones. To ensure that

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332 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s these varieties maintain their distinctive features from one generation to the next, horticulturists propagate them by grafting. Apple trees once grew fairly large, but with the dwarfing rootstocks available today, they are much smaller and thus more easily cultivated at home. In addition to the apple, there are about forty species of Malus worldwide, all in temperate areas of the northern hemisphere. Eastern Asia has the greatest diversity. Iowa has a single native species, the prairie crabapple, whose botanical name means “of Iowa,” reflecting its discovery here. It grows in open woods, prairie remnants, brushy places, old fields, and similar habitats through most of the state. A double-flowered form called ‘Bechtel’s Crab’ is sometimes cultivated. You are more likely to see one of the hybrid crabs that have been developed by horticulturists. These beautiful trees are amazing in their variety, including their shape and branching, which range from broad and wide-spreading to narrow and upright. There are even weeping forms for people who appreciate that unusual habit of growth. Crabapples also vary tremendously in fruit. Those of our native American species look very much like small green apples. Cultivated crabapples are much more diverse, ranging in size from a golf ball to a small pea and in color from yellow to orange to red. Most modern cultivars have been bred for small fruits, as people don’t appreciate the larger, messier fruits of older varieties. Crabs are planted primarily for their showy flowers, but their fruits are also ornamental and worth considering when selecting a tree. In some cultivars the fruits persist into the winter, providing many weeks of color. Birds like crab­ apples too, another reason to include these trees in our landscapes. Squirrels and small mammals also relish them. As a group, the crabs are susceptible to a great many diseases and insect pests. While one can spray for these, it is more practical to use resistant cultivars. Common leaf problems include scab, powdery mildew, and rust. While these are not fatal, they can mar the appearance of the trees and cause premature defoliation. Fire blight is more serious, causing dieback and even death of trees. Because of certain similarities among the apples, crabapples, and pears, some botanists place them all in the genus Pyrus. This might seem odd considering the obvious differences between edible apples and pears, but some pears look very much like apples, for example, the Asian pear now available in many supermarkets.

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Crabapples are diverse in their form, foliage, fruits, and other features. Both red- and whiteflowered types are available.

Some kinds of crabapple are susceptible to fungus diseases, which mar the appearance of their leaves and cause premature defoliation.

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334 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s In the following table, Jeff Iles of Iowa State University has compiled the best crabapples for Iowa. Taxon

Form

Foliage

Flower

Fruit

‘Adirondack'

upright (inverted cone)

dark green

white

orange-red, 1/2" 18/10'

Height/Width

fuchsia-pink

burgundy, 3/8"

10/8'

dark purplered

pinkish red

deep red, 1/2"

16/22'

light green

white

gold, 1/4"

8/5'

light green

white

scarlet, 3/8"

15/20'

Limitations: slow-growing ‘Camzam' (Camelot)

rounded/compact dark green/ burgundy

Limitations: not much late-season interest ‘Cardinal'

broad-spreading

Limitations: none known ‘Cinzam' (Cinderella)

rounded, upright

Limitations: slow-growing ‘David'

rounded

Limitations: alternate bloom, light apple scab noted, fruit mummies persist until spring ‘Donald Wyman'

rounded

medium green

white

bright red, 3/8"

20/20'

pink-white

amber, 3/8"

12/20'

medium green

white

red, 1/2"

15/12'

purple cutleaf/ orange-red in fall

pinkish red

red, 1/4"

20/15'

medium green

white

gold, 3/8"

10/8'

Limitations: apple scab noted, fruit mummies persist until spring floribunda

spreading/ irregular

medium green

Limitations: unimpressive display of fall fruit ‘Jewelcole' (Red Jewel)

pyramidal

Limitations: none known ‘jfs-kw5' upright (Royal Raindrops)

Limitations: none known ‘Lanzam' (Lancelot)

oval

Limitations: flowers and fruit borne on interior of tree, which diminishes their ornamental effect ‘Louisa'

weeping

dark green/ glossy

Limitations: fruit are ornamentally insignificant

rose-pink

amber, 3/8"

10/15'

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f l o w e r i n g t r e e s 335 Taxon

Form

Foliage

Flower

Fruit

Height/Width

‘Orange Crush'

rounded

purplish green

rose-red

red, 3/8"

15/15'

medium deep pink green/yellowapricot fall

red, 3/8"

15/15'

purple turn­ ing reddish green

dark red, 1/2"

20/20'

maroon, 1/2"

20/20'

golden-yellow, 1/4"

20/15'

Limitations: none known ‘Prairie Maid'

rounded

Limitations: none known ‘Prairifire'

rounded

pinkish red

Limitations: requires pruning to correct overcrowded branching ‘Purple Prince'

rounded

purple turning bronzegreen

rose-red

Limitations: heavy fruit production may weigh down branches ‘Schmidtcutleaf' (Golden Raindrops)

upright

medium green/deeply cut

white

Limitations: alternate bloom, fire blight has been reported

Mulberries, Morus L. White Mulberry, M. alba L. Red Mulberry, M. rubra L. You probably know the mulberry, even if you spend most of your time in town. It seems to turn up everywhere that isn’t cultivated or mowed, including hedges, shrubbery, perennial gardens, vacant areas, and the foundations of buildings. Oddly enough, the trees you commonly see are not native to Iowa, while the trees that are native here can be difficult to find. Of the two species growing wild here, the more common is the white mulberry from China. A favorite food of the silkworm, it was introduced to America in colonial times in an effort to start a silk industry here. That venture failed, but our native birds loved the fruits and spread the tree far and wide. Our other species, the red mulberry, is more particular where it grows and has a smaller range. An understory tree, it can be found in floodplains, ravines, and moist sheltered slopes in the southeastern half of Iowa. Its unusually large

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336 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s leaves, which may be up to 9 inches long, make it easy to spot in the forest. Its wood, which is hard, heavy, and durable in the soil, is used occasionally for fence posts and furniture. Both species are unusual in their variably shaped leaves, which may be unlobed or lobed. Unlobed leaves are more common in the shade and lobed in the sun, but both types often occur on the same tree. The two species differ in the size and hairiness of the leaves (see pages 174–177), but one can find trees whose leaves are intermediate between the two and are presumably hybrids. The blackberrylike fruits of mulberries ripen in early to midsummer. Those of the white mulberry may be white, red, or dark purple, while those of the red mulberry are consistently dark. Many kinds of wild birds and mammals appreciate them, including robins, orioles, catbirds, cardinals, wood thrushes, waxwings, opossums, skunks, squirrels, and raccoons. People gather them too, using them for pies, jellies, and wines. Some mulberries never fruit, because the trees are either male or female. Female trees are a nuisance near sidewalks, driveways, and streets because the fruits are so messy when they fall. Male trees, on the other hand, make nice shade trees when properly pruned and shaped. In cultivation they grow 30 to 50 feet tall with rounded crowns.

Ironwood or Hop Hornbeam, Ostrya virginiana (Mill.) K. Koch

Few people know the ironwood, though it is one of our most common trees (see photo on page 303). Small and nondescript, it grows unobserved in the understory of our upland woods, where it is often the most abundant tree. If it stands out at all it is during the winter, when its faded brown leaves cling tightly to its branches. Ironwood is named for its exceptionally hard, heavy wood. This is of little commercial importance because the tree is so small, but it had a variety of interesting historical uses including levers, mallets, wedges, tool handles, axles, sled runners, ox yokes, and kitchen utensils. Ironwood is also an excellent fuel wood. Though resembling an elm, the ironwood is more closely related to the birches and hornbeams. Like most trees in that family, it has winter catkins at the tips of its twigs. Its fruit, a tiny nut or nutlet, is enclosed in a papery sac that

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f l o w e r i n g t r e e s 337

also persists into winter. These are grouped in short clusters resembling those of the hops plant, hence the common name of hop hornbeam. Ironwood is a tough and adaptable tree that grows well in sun or shade. Though slow to establish after transplanting, it develops into a handsome and very durable small shade tree that is seldom bothered by diseases or insects. When grown in the open, it usually develops a broad, rounded crown and attains a height of 25 to 40 feet. Its leaves turn yellow in autumn.

Amur Corktree, Phellodendron amurense Rupr. This medium-size tree from northeastern Asia is occasionally used for landscaping in Iowa. Tough, adaptable, and easy to grow, it is picturesque in winter with its thick, corky bark and wide-spreading branches. Its leaves turn light yellow in autumn. Corktrees are dioecious, with the male and female flowers on separate trees. The small, berrylike fruits of female trees are eaten by birds, and as the seeds germinate readily, the trees can become weeds in woods and other natural areas. It is thus best to plant male cultivars only.

Sycamore, Platanus occidentalis L. The sycamore is one of our largest and most distinctive native trees, one of just a few survivors of an ancient and once widespread family. With its large, platesize leaves and striking bark, it stands out at all times of year. In nature the sycamore is usually found in bottomlands, but like most trees of such habitats, it adapts well to other sites. It is very tolerant of urban conditions and, where space allows, is often planted along streets. Among the fastest-growing of our native trees, it develops a massive trunk and a broad, spreading crown up to 100 feet tall. Though a very handsome tree, the sycamore does have its limitations for landscaping. It is definitely messy, shedding bark and dropping leaves almost continually and offering little color in autumn. A fungal disease called anthrac­ nose often kills the emerging leaves and shoots in spring, so the trees appear dead and offer little shade until a new crop of leaves appears later. The degree of infection varies greatly from year to year and is most severe when the weather is cool and wet in spring during the two-week period following leaf emergence.

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338 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s

Sycamore is a majestic tree with bright white upper bark.

Anthracnose is rarely fatal in itself, but repeated bouts can weaken a tree, increasing its susceptibility to other diseases, insect pests, and winter injury. For a fast-growing tree, sycamore has a fairly hard and heavy wood. The wood is used for veneer, flooring, the concealed parts of furniture, millwork, plywood, pallets, and pulp. Butcher block is one of its most distinctive uses, because it has interlocked grain and is difficult to split. Sycamore is sometimes called plane tree, as are its relatives in Europe and Asia. The eight species of this genus are the sole survivors of an ancient family, the Platanaceae. More than thirty genera grew in the days of the dinosaurs and early mammals, when these trees comprised a significant part of temperate and subtropical forests. The London plane tree [Platanus ×acerifolia (Ait.) Willd.] is a hybrid between the sycamore and the oriental plane tree that is sometimes planted in Iowa. It differs from sycamore in having two seed balls per stalk instead of one, in its sometimes greener bark, and in the more deeply lobed leaves of some of its cultivars.

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f l o w e r i n g t r e e s 339

Cottonwoods, Aspens, and Poplars, Populus L. Eastern Cottonwood, P. deltoides Bartr. Quaking Aspen, P. tremuloides Michx. Bigtooth Aspen, P. grandidentata Michx. Lombardy Poplar, P. nigra L. var. italica Muenchh. White Poplar, P. alba L. Balsam Poplar, P. balsamifera L. The trees of the genus Populus are a diverse lot, with no single common name that ties them all together. Though obviously different in foliage and bark, they have many similarities in the way they live and grow. Wherever you go in Iowa, you will encounter these abundant and familiar trees. One similarity is the way they reproduce. The flowers are borne in tail-like clusters called catkins, with the male and female on separate trees. Pollinated by wind, the flowers are small, lack petals, and often go unnoticed when they appear in early spring. The catkins bearing male flowers soon fall from the tree, but those with female flowers remain until summer, when their small, flask-shaped seed pods mature. Tiny for a tree and sporting light, cottony hairs, the seeds are caught by the wind and blown away. Living only a few days, the seeds must find a new home quickly. If the spot where they land has moist bare soil and sun, they sprout and begin to grow. The trees are usually prolific — as anyone who has a female cottonwood knows  — so where there is one seedling there are often many. Their growth is among the fastest of trees, producing a good-size sapling in only a few years time. All Populus reproduce like this, but once established, some increase their numbers in another way. Aspens and some poplars sprout profusely from their roots, forming new stems at increasing distances from the parent tree. In this way large groves can form, all descended from a single seed. Through both seeds and suckers, Populus are important pioneer trees, colonizing land that has been made bare by flooding, fire, or human disturbance. Sun-loving and short-lived, the trees cannot reproduce in the shade they create and thus do not persist indefinitely. They do, however, create new forests where other, more shade-tolerant and longer-lived trees can grow. As the Populus trees grow old and die, they are replaced by these longer-lived species. Populus species also resemble one another in their wood, which is light, soft, usually straight-grained, and relatively weak. Most species are used for pulp,

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340 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s

The eastern cottonwood is common along streams, in low pastures, and in other moist places, growing to be one of our largest trees. A rust disease sometimes causes its leaves to drop early.

with aspen especially valued for high-grade paper. Other uses include veneer, lumber, pallets, boxes, and crates. Among our native species, the eastern cottonwood is most widespread and probably the best known. With its massive trunk and tall, broad-spreading crown, it is our largest and one of our most impressive native trees. Easy to grow and readily available along rivers and streams, it was widely planted by

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the farmers and townspeople who settled the treeless prairies of Iowa. Today it’s not held in such high esteem, but it is still a good choice for parks, reforestation, fuel-wood plantations, and even as a shade tree where there is room for it to grow and its limitations are understood. And what are those limitations? For one, the cottonwood has weaker wood than many other trees, meaning more litter after windy or icy weather. Though living longer than other Populus and tending to age more gracefully, it is still short-lived compared to oaks, hickories, and many other native trees. The foliage can be a beautiful yellow in autumn, but a fungal disease called leaf rust often causes the leaves to drop early, before the color can develop. Lightning is another concern, because the cottonwood is often the tallest tree around. Cottonwoods grow well when transplanted to dry upland sites, but wild trees are almost always found in moist places. In river bottoms and along lakeshores, cottonwoods form forests with willows, silver maple, green ash, and other trees. One can sometimes find a long row of cottonwood seedlings on a beach, mud flat, or sandbar, clearly marking the location of the shoreline the previous June. Several variations of the cottonwood can be found in Iowa. A naturally occurring form called the Plains cottonwood [subspecies monilifera (Aiton) Eckenw., also known as var. occidentalis Rydb. and P. sargentii Dode], with yellow twigs and hairy-edged bud scales, occurs infrequently in western Iowa. The male cultivar ‘Siouxland’ is sometimes planted; it has attractive dark green leaves and is resistant to rust but is sometimes attacked by canker. Hybrids between the cottonwood and other poplars, for example, the Eurasian black poplar (P. nigra L.), are used for conservation plantings and landscaping. Two other native species, the quaking and bigtooth aspens, are found mainly in the northern part of the state. We normally associate these trees with the North Woods or Rocky Mountains, so some people are surprised to learn they also grow wild in Iowa. Unlike their cousin the cottonwood, they usually grow in upland sites. Both are appropriately named. Quaking aspen has small, roundish leaves with long, flattened stalks that seem to quiver and rustle incessantly. The leaves of bigtooth aspen are similar but have much larger and fewer teeth. The foliage of both is beautiful in autumn, turning a bright golden-yellow as the maples are losing their leaves and the leaves of the oaks are changing from reddish to brown. Quaking aspen is often confused with paper birch, especially in the winter

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Aspen trees spread by underground runners, and in this way a single seedling can become a whole grove of trees.

or when viewed from a distance, as both trees have chalk white bark. To distinguish the two, remember that birch bark separates into papery strips and appears somewhat rough-hewn, while aspen bark is smooth and tight-fitting. Also, birch leaves have short, rounded stalks and do not tremble in the wind. Aspens are an important source of food and cover for wildlife, especially in more northern latitudes where they are among the most common trees. Their foliage and twigs are eaten by deer and rabbits, and their buds are a mainstay of the ruffed grouse’s winter diet. Beavers relish the inner bark and use the trunks in their dams. Because aspens grow rapidly and are beautiful throughout the year, one might expect them to be useful trees for landscaping. Unfortunately, they are short-lived for a tree, tend to grow rather tall and gangly, and are subject to a number of pests. Root suckers are another problem, especially when the trees are grown in gardens. All things considered, it seems best to leave the aspens in their natural haunts and appreciate them there. In addition to the above, several poplars are cultivated in Iowa. Two of these can be found growing wild in parts of the state. Resembling the cottonwood in leaf though not in form, is the spirelike Lombardy poplar. This introduced tree is planted for borders, screens, and windbreaks, although its usefulness is limited by its susceptibility to canker, which can greatly shorten its life span. The Eurasian white poplar is a large, handsome tree with white upper bark, leaves that are often strongly whitened on their lower surface, and a broad,

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spreading crown. As an ornamental tree its characteristics are similar to those of the cottonwood, except that it colors very little in autumn. Also, it can sucker quite profusely, which limits its usefulness in many situations. The cultivar ‘Pyramidalis,’ commonly called the Bolleana poplar, has a columnar form resembling that of the Lombardy poplar. The balsam poplar is a characteristic tree of America’s North Woods, easily identified by its large, ovate leaves with a brownish cast beneath. Wild-growing trees, presumably escapes from cultivation, have been reported from moist woods and edges in a few of Iowa’s northern counties. A naturally occurring hybrid poplar, P. ×rouleauiana Boivin (P. alba ×P. grandidentata) has been found in southeastern Iowa. This has been inves­ tigated for possible forestry use including biomass production.

Cherries and Plums, Prunus L. Black Cherry, P. serotina Ehrh. Chokecherry, P. virginiana L. Pin Cherry, P. pensylvanica L. f. Sand Cherry, P. pumila L. Dwarf Cherry, P. besseyi Bailey American Plum, P. americana Marsh. Canada Plum, P. nigra Ait. Goose Plum, P. hortulana Bailey Big-tree Plum, P. mexicana S. Watson Peach, P. persica (L.) Batsch Bird Cherry or May Tree, P. padus L. The cherries and plums are diverse in many ways, but they do have one obvious thing in common: edible fruits with a single large seed in the middle. They are also a delight in spring, beloved around the world for their beautiful flowers. Botanists place them in the genus Prunus along with the peach, apricot, and almond. Most cherries and plums are valued primarily for their fruits, but one Iowa native, the black cherry, is appreciated most for its wood. This has been admired since colonial times for its beautiful red-brown color and attractive luster. Cherry is also strong, moderately hard, and durable, with a fine and even texture. It works easily, takes a fine finish, resists shock, shrinks little when first

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344 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s dried, and seldom warps or checks during seasoning. Important uses include fine furniture, scientific instruments, piano actions, patterns, and novelty items. Native black cherry occurs in upland woods, wood edges, and fencerows throughout most of Iowa, becoming less common to the northwest. In moist, fertile, well-drained soils it can grow quite large, up to 2 feet in diameter, which makes this species a giant among the cherries and plums. Look for it where you see oaks, hickories, white ash, aspens, and ironwood. Black cherry is valuable for reforestation in Iowa, and while seldom used for landscaping, it is an attractive tree that could be more widely planted. It grows fairly rapidly, eventually forming an oval to spreading crown of slightly drooping branches. The leaves usually turn light yellow in autumn. A much smaller cherry, the chokecherry, is native throughout Iowa in upland habitats. It resembles the black cherry in flower and fruit but differs in its smooth bark and broader, more sharply toothed leaves. Often shrubby and colonial, it rarely reaches 30 feet when a tree.

(Right) Chokecherry’s small white flowers appear in racemes in spring. The flowers of black cherry are similar. (Below) The black knot fungus produces hard black galls on chokecherries and related trees, causing dieback of branch tips.

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Chokecherry is useful for wildlife plantings and can be incorporated into naturalistic landscapes as well. It is, unfortunately, susceptible to two diseases that cause dieback and decline, neither of which is curable. Black knot is a fungal disease that produces hard black structures resembling dried feces on the twigs and branches. As these structures enlarge, they girdle the stem and cause the terminal portion to die. Cherry X disease, so called because its cause was unknown for many years, is produced by a phytoplasma that is spread by leafhoppers. It causes a gradual loss of vigor leading to decline. Premature autumn color is the most obvious symptom. Three other cherries are native to Iowa but less commonly seen. Pin cherry is a small tree of woods and clearings in northeastern and north central Iowa, though common only in the northeastern corner. Sand and dwarf cherries are prostrate shrubs, both rare in Iowa. Sand cherry grows in open, sandy habitats in the northern and eastern parts of the state, while dwarf cherry is limited to rock outcrops in extreme northwestern Iowa. The fruits of our wild cherries are small, tart, and juicy. They are much appreciated by chipmunks and birds, including pheasants, catbirds, robins, brown thrashers, cedar waxwings, several kinds of thrushes, and even woodpeckers. Their hard pits pass undamaged through the birds’ digestive tracts, producing new trees in woods, thickets, fencerows, and other places frequented by birds. Wild cherries can also be used for making wine and jam. Iowa is also home to four species of wild plums. The one most commonly seen is the American plum, which is native throughout the state. It would be difficult to find a wood edge, fencerow, or railroad right-of-way that did not harbor at least one thicket of this thorny and often crooked little tree. Though inconspicuous most of the year, the plum is a standout in spring, when it livens the countryside with its showy, fragrant flowers. It is a display worthy of some carefully nurtured ornamental tree, not what one would expect from a clump of brush that came up spontaneously. Over the summer months, the flowers continue their development into small, edible plums. When ripe in September, these have a juicy yellow flesh that varies considerably in sweetness from one tree to the next. The skin, however, contains an astringent that gives the fruits a sharp bite when eaten. American plum is useful to wildlife but not for the reason one might expect. Its fruits, though high in food value, are eaten by just a few kinds of animals. The plum’s greatest value lies in the nesting and protective cover that its dense, thorny branches provide. Its resistance to drought, ability to grow well in a

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Though inconspicuous most of the year, wild plum stands out in spring.

variety of soils, and tendency to form thickets make it suitable for windbreaks and erosion control, too. Where its suckering habit will not be a problem, the plum can also be used for naturalistic landscaping. Iowa’s other native plums include the Canada plum, which grows on steep, wooded slopes in the extreme northeast and locally elsewhere; the goose plum, which occurs in Lee and Van Buren counties; and the big-tree plum, found here and there throughout the state. The peach, which differs from plums in its elongated leaves and fuzzy fruits, is grown in the warmer parts of Iowa and occasionally escapes to roadsides and fencerows. Several other kinds of cherries and plums are grown for fruit or used for landscaping in Iowa. Ornamental trees include the bird cherry or May tree, the Shubert or Canada red cherry, and various purple-leaved plums. The bird cherry, which was introduced from Eurasia, closely resembles the chokecherry but has bigger flowers and grows larger in size, to 30 to 40 feet. Unfortunately, it is also susceptible to black knot, sometimes to the point of being killed or seriously disfigured by the disease. The Shubert cherry, a cultivar of chokecherry, is a vigorously growing tree of pyramidal habit, maturing at a height of 20 to 30 feet. Its leaves are green at first but change to dark reddish purple.

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The purple-leaved plums, whose leaves are purple from the start, are attractive small trees but prone to borers and are short-lived.

Hoptree, Ptelea trifoliata L. Despite its name, hoptree rarely grows to be a tree, at least not in Iowa. A large shrub, it is native to wood edges, wooded stream banks, rocky bluffs, and low, sandy places in the southeastern and extreme east central parts of Iowa. Plants are occasionally found growing wild in the central part of the state, but it is not known if these are native or escaped from cultivation. The leaves of hoptree resemble those of poison ivy, but the terminal (middle) leaflet is not stalked. Its elmlike fruits are also quite unlike those of poison ivy. The fruits contain a bitter principle and were once used as a substitute for hops.

Callery Pear, Pyrus calleryana Dcne. For years pears were grown almost exclusively for fruit. More recently, the popularity of pears for landscaping has increased. Most widely planted are the cultivars of Callery pear, which is native to China. These trees offer showy white flowers in spring; attractive, dark glossy leaves throughout the summer; and good red and crimson foliage in late fall, after many other species have lost their leaves. The fruits are small for a pear — about 3/8 inch in diameter — and yellowish brown in color. Cultivars differ in form, bloom time, resistance to disease, and other characteristics. They are propagated by grafting. ‘Bradford’ was the first cultivar introduced and was widely planted. Growing 30 to 50 feet tall at maturity, it develops a broadly pyramidal to rounded crown. It has proved to be a tough and adaptable tree that grows well in urban conditions and resists fire blight, a serious disease of pears. Unfortunately, ‘Bradford’ develops weak crotches that may split in storms, and for this reason it is falling out of favor. ‘Chanticleer,’ also known as ‘Glen’s Form’ and ‘Cleveland Select,’ is one of the better regarded of the more recently introduced cultivars. Unfortunately, the Callery pear is proving invasive in parts of the United States, particularly the East. Cultivars are self-incompatible, so where only one kind is planted, the trees rarely fruit. Where more than one kind is grown nearby, however, or the understock of a grafted plant is allowed to grow, cross

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348 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s pollination can occur, resulting in fruit with viable seed. Birds eat the fruits and spread the seeds to wild areas, where they grow and displace native species. Escaped trees have now been reported from more than half the states, including Michigan, Illinois, and Missouri in the Midwest. Iowans should watch for wild trees and remove them if found.

Oaks, Quercus L. Bur Oak, Q. macrocarpa Michx. White Oak, Q. alba L. Swamp White Oak, Q. bicolor Willd. Chinkapin Oak, Q. muhlenbergii Engelm. Dwarf Oak, Q. prinoides Willd. Post Oak, Q. stellata Wangenh. Overcup Oak, Q. lyrata Walt. English Oak, Q. robur L. Red Oak, Q. rubra L. (Q. borealis Michx.) Black Oak, Q. velutina Lam. Pin Oak, Q. palustris Muenchh. Hill’s Oak (Northern Pin Oak), Q. ellipsoidalis E. J. Hill Shingle Oak, Q. imbricaria Michx. Blackjack Oak, Q. marilandica Muenchh. The oak is Iowa’s state tree, which should not surprise anyone who spends much time outdoors. Oaks are ubiquitous and often dominate the woods where they grow. No other group of trees is more important to people and wildlife. Twelve species of oaks are native to Iowa, growing in a variety of habitats. Some are confined primarily to bottomlands, while others grow mostly in uplands. A few seem at home most anywhere. Many adapt well to cultivation, as do several introduced oaks from Europe, Asia, and other parts of North America. Depending on its habitat, the same species of oak can have different growth forms. Forest-grown trees are tall and straight, attaining heights of 80 to 100 feet or more. Open-grown trees develop rounded crowns that are often as wide as tall. The presence of such trees, with their low, wide-spreading branches, indicates that an area was originally prairie, savannah, or pasture, even if wooded now.

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When given ample room to spread, oaks can grow wider than tall.

When European Americans first came to Iowa, they found oaks growing in open groves like this one.

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350 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s Acorns, the nuts of oaks, are a dietary staple of a great many game animals and songbirds. Turkeys, wood ducks, raccoons, squirrels, chipmunks, blue jays, nuthatches, grackles, and several kinds of woodpeckers are a few of the species that depend on acorns for a significant part of their diet. The prevalence of oaks in Iowa woodlands also makes these trees valuable as shelter and nesting cover. Overall, oaks are the most important group of trees for wildlife. The commercial value of oaks is due in part to their sheer abundance, but even if they were scarce, they would be esteemed for their hard, strong, and beautiful wood. The list of products manufactured from oak is long, but among its most important uses are furniture, veneer, flooring, railroad ties, mine timbers, and barrel staves. Oak is also an excellent fuel. Iowa’s oaks sort naturally into two groups, the white oaks and the red oaks. The white oaks (section Quercus) have leaves with rounded lobes or large teeth. Their acorns mature in a single growing season. White oak wood is light brown to dark brown in color, and its pores (vessels) are blocked with small plugs called tyloses that make the wood watertight and thus useful for wine casks and whiskey barrels. White oak is also very resistant to decay. The leaves of red oaks (section Lobatae) are lobed in most species. The most distinctive feature of this group is the short bristle that occurs at the tip of each leaf or leaf lobe. The acorns require two growing seasons to mature. The pinkish or reddish brown wood has open pores without tyloses. It is less resistant to decay but, when treated with preservatives, is used for ties, timbers, and similar products. Oak leaves vary in shape among trees of the same species, even on the same tree, but you can usually identify trees by leaves alone. If there is any doubt, check the tree’s acorns, as they are very distinctive. Buds and bark can also be helpful in separating species. Oaks often hybridize, which can further complicate identification. This is especially common where species reach the edge of their natural range, for example, blackjack oak in southern Iowa. Trees in the white oak group can cross with other whites, and red oaks with other reds, but species from the two groups do not naturally hybridize. Most hybrids are intermediate between their two parents. The tiny green or yellowish flowers of oaks appear when the leaves are unfolding in spring. The male flowers are arranged in catkins and disperse their pollen by wind. The female flowers, which are located in the axils of the leaves, occur singly or in small clusters. The small, bright red pistil of each is surrounded by a series of tiny scales that eventually become the acorn-cup.

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The bark of white oaks (right) is light ashy gray, the bark of red oaks darker.

Oaks are normally long-lived, durable trees, but they can be very sensitive to changes in their woodland environment. When buildings and roads are constructed in wooded areas containing oaks, it is especially important to minimize disturbance to the forest soil. Injury to the root system through digging, filling, or soil compaction can cause the decline and eventual death of a mature tree, even if no harm is done to the trunk and branches. For information on how to protect trees during construction, see Iowa State University Forestry Extension publication PM909, “Preventing Construction Damage to Trees,” http://www.extension.iastate.edu/forestry/publications/list.html. Oak wilt, a fungal disease of oaks similar to Dutch elm disease, occurs here and there in Iowa. Although it can kill trees, past outbreaks have remained localized and have not caused a pandemic as did Dutch elm disease. Trees in the red oak group are the most susceptible and usually die soon after they are infected. Oaks in a weakened condition from injury or drought may die from other causes, including cankers, shoestring fungus (Armillaria), and insect borers, so oak wilt should not be automatically blamed when a tree dies. Other oak problems include leaf spots, galls, and various leaf-chewing caterpillars. None of these conditions is immediately life-threatening, although defoliation by gypsy moths can weaken trees, and galls sometimes cause dieback of twigs.

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White Oaks The white oak group in Iowa is represented by five native trees and one native shrub. Another from Europe is sometimes planted. Bur oak is the most widely distributed, occurring in almost every county. The legislature did not name a particular oak as our state tree, but if any is deserving of the honor, it is this one. Bur oak grows primarily in uplands, though it can also be found on stream terraces and floodplains. It is the most abundant tree in much of western and north central Iowa, often forming pure stands. In other parts of the state it is a bit less conspicuous, sharing the woods with hickories and other oaks. Before European Americans arrived, bur oak played a dynamic role in the Iowa landscape. It tolerated dryness better than most trees, and with its thick, corky bark, it was resistant to fire. This allowed it to grow in the open among the prairie grasses. When the settlers arrived from the east, they found open, park-like stands of bur oaks to be a conspicuous feature of the landscape. These stands, which they called oak groves or oak openings, were favored sites for homesteads. Later, when cultivation brought an end to the prairie fires, many of the uninhabited oak openings became overgrown with brush and weedy trees. The bur oak’s tolerance of dry conditions is due in large part to its extensive root system. Seedlings immediately produce a deep taproot, which may grow 5 feet long in its first season. Mature trees have branch roots that extend 20 to 60 feet horizontally before growing downward. The root system may weigh as much as the aboveground part of the tree. Though tough and potentially long-lived, bur oak is not trouble-free. A new foliage disease, called bur oak blight, has been infecting trees since the early 2000s. According to research by Thomas Harrington at Iowa State University, this is caused by a new strain of the Tubakia fungus, which is usually innocuous in oaks. Infections do not become apparent until late in the growing season, when the leaves turn brown and fall from the trees. It is common to see healthy and infected trees growing side by side. As this book goes to press, it is uncertain how the disease spreads or what its long-term effects will be. Just as bur oak is associated with prairies, white oak is associated with forests. Throughout much of eastern, southern, and central Iowa, it is one of the most common upland trees. It is also one of the longest-lived, with some individuals more than 400 years old. The most aged trees are not necessarily the

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The attractive figure of quarter-sawn oak makes it popular for furniture and cabinetry.

largest and are often twisted and gnarled on the ridges where they grow. Because they were not so desirable in form, they were spared from harvest when Iowa’s original woodlands were cut. White oak is well known for its useful wood. The attractive figure of quarter-sawn lumber has made it popular for paneling and furniture, particularly for desks and tables. White oak’s durability makes it useful for mine timbers, railroad ties, and posts and, because it is watertight, for making barrels. In the days when people traveled mostly by sail, it was valued for building ships, including the famous warship Old Ironsides. Many pioneer homes were constructed of beams, lumber, and shingles of this tree. The leaves of white oak turn a rich wine color in early October, eventually fading to a dull reddish brown and finally to a light brown. The dried leaves may remain on the branches well into winter. The picturesque shape of this tree and its light ashy bark make it one of our most attractive native trees during the winter months. The white oak’s beauty, longevity, and durability make it an excellent choice for landscaping, although it is seldom planted because it grows slowly and is difficult to transplant. Great care should be exercised when building homes in wooded areas, as the roots of this species and other native oaks are very sensitive to soil disturbance. Though not much bothered by disease, white oak is injured in some places and in some years by anthracnose and tatters. Anthracnose is a fungal disease

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354 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s that infects the leaves in spring, causing unsightly brown lesions along or bounded by veins. Badly infected leaves become curled and distorted, especially on lower branches. Tatters removes most of the green tissue between veins, as if the leaves had been eaten by insects. Its cause is not certainly known. Both conditions occur early in the growing season, when trees are the most vulnerable because their energy reserves are low. Though not deadly in themselves, these diseases can weaken trees, particularly if repeated in successive years. If you frequent places where white and bur oaks grow, you may have noticed that the outer bark is missing on some trees, in patches of varying sizes and shapes. This condition, called smooth patch, is caused by fungi growing on the bark. Affected trees are not harmed but look odd compared to normal trees nearby. Two other white oaks, the chinkapin and swamp white, grow in parts of eastern, southern, and central Iowa. Their leaves are similar in outline, with large teeth instead of lobes. They are otherwise quite different trees, especially in their habitat. Chinkapin oak is most common in upland woods, often in the

A fungus sometimes causes the outer bark of white oaks and bur oaks to slough off, but this does not harm the trees.

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driest of sites. Swamp white oak, as its name suggests, is primarily a tree of bottomlands. Both are handsome trees, useful for landscaping. Chinkapin oak is the more adaptable, tolerating the heavy clay and alkaline soils that trouble some other oaks. Swamp white oak is useful for wet places but can also be planted in sites that are dry, provided the soil is not alkaline. Neither species is particularly colorful in autumn, although the foliage of chinkapin is sometimes an attractive orange-brown. Swamp white is the more interesting in winter, with its flaky bark of differing shades. Chinkapin has a close look-alike in the dwarf oak, which as its name suggests is low and shrubby. Taxonomists disagree as to whether the two are separate species or different varieties of the same species. They can hybridize when growing nearby, producing populations with an intermingling of characteristics. Dwarf oak is native to uplands in southern Iowa and has also been reported from Allamakee County in the northeastern corner of the state. Iowa’s rarest white oak is the post oak. It is native to a few counties in southeast and south central Iowa, where it inhabits dry upland woods with other oaks and hickories. Another species, the overcup oak, was reported near Amana many years ago. It grows naturally in the southeastern United States and is probably not native to Iowa. Other species of white oaks grow in Europe and Asia, and one, the English oak, is occasionally planted in Iowa. In its typical form it is a large and impressive tree, with a short, massive trunk and rounded crown. Horticultural forms include trees with dissected leaves and columnar habits. The species has a broad range, from Spain to Russia, and trees grown in Iowa should be selected from northern sources only.

Red Oaks Six species of red oaks are native to Iowa. There is considerable variation within some species, which along with hybridization can make identification challenging. Red oak is the most widely distributed, growing in all but a few northwestern counties. It is an upland tree, most commonly seen on moist sheltered slopes with hard maples, basswood, bitternut hickory, and other trees. On drier sites, it often occurs with white oak and shagbark hickory. It can grow very large and is an important timber tree.

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356 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s Red oak is adaptable and easy to grow, often a better choice for landscaping than the popular pin oak. Its leaves remain a handsome dark green throughout the summer, then turn red, orange-red, yellow, or reddish brown in autumn. Its growth rate is fairly fast for an oak, up to 2 feet per year when young. Two variations can be found in Iowa, most easily distinguished by acorns. Typical red oaks (variety rubra) have large acorns with saucer-shaped cups that barely cover the base of the nut. Variety borealis has smaller acorns with bowl-shaped cups that cover the lower third of the nut. The extent of their ranges in Iowa is unknown. Black oak is often confused with red oak but can be distinguished by leaf, bud, and acorn. It also frequents drier habitats, being particularly common on ridges and sunny slopes with other oaks and hickories. In eastern Iowa it also occurs on stream terraces and bottomlands where the soil is sandy and very well drained. Though seldom used for landscaping, it has attractive glossy leaves that turn red or reddish brown in autumn. Nicely shaped trees are worth preserving when wooded sites are developed. Unusual black oaks occur in some parts of Iowa and illustrate the problems in oak taxonomy. The typical form found in most of southern and eastern Iowa has large, densely tan-hairy buds and acorn-cups with loosely attached scales. Other trees in eastern and north central Iowa have smaller buds that are sparsely white-hairy and acorn-cups with tighter-fitting scales. Their leaves are also somewhat different in shape. Are these trees really black oaks, or are they hybrids with other species? No one really knows. A third member of the red oak group is more often found in cultivation than in the wild. Pin oak is native to bottomland forests in eastern and southern Iowa, but it has been planted in every county. As a landscape tree, pin oak is prized for its symmetric form and dissected leaves, which under the right conditions can turn striking shades of red and purple in autumn. Like a conifer, its trunk runs unforked to the top of the tree and its crown is pyramidal in shape. Its upper branches point skyward, the middle stay horizontal, and the lower sweep downward, often touching the ground. Unfortunately, cultivated pin oaks are often afflicted with chlorosis. This condition can greatly diminish a tree’s ornamental value and in serious cases may lead to its decline and eventual death. Chlorosis is a complex problem that appears to be caused most often by nutrient deficiencies related to soil alkalinity. Certain nutrients, especially iron and manganese, are less soluble

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A towering red oak near East Okoboji Lake, at the northwest edge of this species’ range in Iowa.

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358 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s in alkaline soils, and roots may be unable to absorb them in sufficient quantities. Drought, salt injury, excessive fertilizer application, and damage to the roots may also cause or contribute to chlorosis. Where soil pH is above 7.5, the best solution is to consider trees other than pin oak. If your existing tree is chlorotic and soil alkalinity is the likely cause, have an arborist examine the tree and advise you on how to proceed. The most lasting treatment is to acidify the soil, apply any micronutrients that are deficient, and create a good environment for root growth by replacing turf under the tree with mulch. If you discover a wild tree in northern Iowa that resembles pin oak, you have probably found a Hill’s oak, also known as northern pin oak. This tree is common in the Great Lakes area and ranges south into Iowa, but it is not well known here. Not everyone agrees that it is a unique species, considering it instead to be a regional variant of scarlet oak. (For more on this issue, see Shepard 2009 and the various floras listed in the bibliography.) Further complicating matters, Hill’s oak is known to hybridize with other oaks including red oak and black oak. Hill’s oak was first described from the Chicago area in 1899 by botanist E. J. Hill, who is honored in its common name. In Iowa it grows primarily in upland woods, often with red oak, which has similar bark but different leaves and acorns. In presettlement times Hill’s oak was reportedly quite common along the prairie-forest border, often becoming shrubby and invading the open prairie with bur oak, hazel, sumac, and other pioneer species. If you go afield in the southern third of Iowa, you might find two oaks with very unusual foliage. The more common of these is shingle oak, whose leaves are not lobed at all. If it were not for its tell-tale bark, buds, and acorns, you might think it’s something other than an oak. Shingle oak is an adaptable species, found in a variety of habitats. Abandoned strip mines, known for their acidic and very inhospitable soil, are among its more unusual homes. It is also used for landscaping in the southern, central, and eastern parts of the state. Young trees are often shaped like pin oak, but mature trees are more typically open and rounded. Their glossy dark green leaves turn yellow or reddish brown in late autumn, then fade to light brown and persist on the tree through most of the winter. The trees are usually trouble-free, but chlorosis and galls are sometimes a problem. Shingle oak is named for an interesting historical use — its wood splits eas-

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Insects cause many kinds of galls on oak leaves. Fortunately, most of them are not harmful.

ily and was rived into shingles and shakes. Today it is relatively unimportant as a timber tree, but its wood resembles that of red oak and is not distinguished from it when sold. Blackjack oak is native to a few counties near the Missouri border, growing locally in open, sandy areas and dry upland woods. It is a small, straggly tree, rarely more than 30 feet tall. Its peculiar leaves resemble an upside-down bell, with tapered bases and broad, shallowly three-lobed tops. Iowa’s blackjacks cross freely with black oak, producing a hybrid named Quercus ×bushii. In some places the hybrids are more common than the blackjack. Their leaves are quite variable in shape but usually have three large terminal lobes and two smaller lobes near the base. They are usually similar to blackjack oak in growth form. Other trees from the red oak group are sometimes planted in Iowa, including the scarlet oak (Q. coccinea Muenchh.) and Shumard oak (Q. shumardii Buckley). Both are native to the southern and eastern United States.

Some Oak Relatives Two relatives of the oaks are native to the eastern United States and sometimes planted in Iowa. Both have suffered greatly because of introduced diseases. American beech, Fagus grandifolia Ehrh., is an important forest tree throughout most of the East. With its smooth gray bark and handsome leaves, it is among the most beautiful of American trees. Unfortunately, many

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360 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s beeches are being killed by beech-bark disease, which has been spreading through the northern part of the range since it was accidentally introduced around 1890. Trees in western Michigan are now infected, near the west edge of the beech’s range. American chestnut, Castanea dentata (Marsh.) Borkh., has been essentially wiped out in its natural range by chestnut blight. Occasional uninfected trees are found in Iowa and other states, although the long-term survival of such trees is not assured, as the blight may simply have not arrived in those places. The American Chestnut Foundation (www.acf.org) is working to develop resistant trees, so the chestnut can once again be an important part of the American landscape.

Common Buckthorn, Rhamnus cathartica L. Children are sometimes admonished to speak positively about someone or not at all, but it is hard to say anything good about the common buckthorn. Imported from Europe for hedges, it has become a terrible weed in Iowa woodlands. Buckthorn is also the alternate host of the oat rust disease and is considered a primary noxious weed in Iowa. Buckthorn is treelike in form if not in stature, usually with a single stem growing 6 to 25 feet tall. Like the honeysuckles, which often grow with it, it can form dense tangles that shade out wildflowers and prevent trees from reproducing. Its purple-black, berrylike fruits are eaten by birds, which disperse the seeds to new locations. Buckthorn is most easily controlled in late autumn, as its dark green leaves persist longer than those of native trees and shrubs, making it easier to find. It is best to seek out and destroy the female (berry-producing) plants first, to remove the source of new seedlings. Immediately after the stems are cut, the stumps should be treated with an appropriate herbicide so the plants don’t resprout the next year. Two other Eurasian buckthorns occasionally escape from cultivation in Iowa. Dahurian buckthorn (R. davurica Pallas) and glossy buckthorn (R. frangula L.) are aggressive weeds in some states and should be removed when they are found here. The Eurasian buckthorns have given the genus Rhamnus a bad name, but two shrubby species are native in Iowa and not weedy. R. lanceolata Pursh, called lanceleaf buckthorn because of its narrow leaves, grows in wooded areas

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in the southern half of the state. Alder buckthorn, R. alnifolia L’Hér., occurs on rocky, cold-air slopes in the northeastern corner of Iowa.

Sumacs, Rhus L. Staghorn Sumac, R. typhina L. Smooth Sumac, R. glabra L. Fragrant Sumac, R. aromatica Aiton Poison ivy, R. radicans L. [Toxicodendron radicans (L.) Kuntze] Sumacs are common sights throughout Iowa, forming colonies along the edges of woods and in open areas nearby. They are particularly noticeable in fall, with their bright red and crimson leaves, and in winter with their stout branches and distinctive red fruits. Two of our native species are treelike in form. The larger of these is the staghorn sumac, which usually grows 15 to 25 feet tall but can reach 40 feet. Staghorn is an appropriate name for this little tree, for its stout, erect branches look much like the antlers of a stag, even to the soft

The bright red fruits of sumacs are a familiar sight along the edges of woods and in other open areas across Iowa.

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362 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s hairs or velvet that covers them. It is native locally in northeastern Iowa and occasionally planted, often in its cultivar forms, which have dissected, fernlike leaves. Smooth sumac is smaller and more common, native everywhere in Iowa. It often forms huge colonies by suckering, with the original, tallest stems in the center. Though mostly beneficial because of its usefulness to wildlife, it can be weedy in prairies. Two other sumacs are native to southern Iowa. Fragrant sumac is a low shrub with glossy, three-parted leaves, growing wild in the southeastern part of the state and cultivated elsewhere. The shining sumac (R. copallina L.), rare if it still exists in Iowa, was reported from a few counties in the 1930s and 40s. All sumacs are tough and easy to grow and thus useful for conservation plantings. They are also good choices for naturalistic landscaping. Sunny, well-drained sites are best, in places where their colonizing habit will not be a problem. All are valuable to wildlife, providing browse for deer and rabbits, good nesting and protective cover, and fruit for songbirds and game birds when preferred foods are scarce. Iowa’s native sumacs are harmless to people, but they are closely related to several poisonous species, all of which have white fruits. Two of these, the poison sumac and poison oak, do not grow in Iowa. Unfortunately, many Iowans are well acquainted with a third — the poison ivy. Though not a tree, poison ivy often grows with trees and even on them, so it is worth covering in a book about trees. Occurring in various forms — as a vine, shrub, or groundcover — and growing in a variety of habitats, it is native throughout Iowa. When a vine it can climb high on the trunks of trees, producing long, straight branches that can be easily mistaken for those of the tree. The skin-irritating principle of poison ivy is carried in a resin found in all parts of the plant. The resin usually reaches a person’s skin through direct contact with the leaves but can also be spread by smoke from burning plants, by touching pets or contaminated clothing, even by handling long-dead plants. Some people are able to touch poison ivy without ill effect, but this “immunity” can vanish at any time. People usually become more sensitive with increased exposure. Though not much appreciated by people, poison ivy is valuable to wildlife. Its small, berrylike fruits are eaten by many birds including flickers and other woodpeckers, catbirds, chickadees, hermit thrushes, quail, pheasants, and turkeys. Deer and rabbits occasionally browse the twigs and stems.

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If you were to examine poison ivy closely (and who but a botanist would do that?), you might notice there are two kinds. The typical variety (var. radicans) occurs throughout Iowa and produces aerial rootlets that allow it to climb trees, although it does not always do so. The other variety (var. rydbergii) grows in northern Iowa only. It spreads by underground runners, producing short, upright, usually unbranched stems with several leaves crowded at the tip of each. Some botanists regard the two as distinct species. Both types can be distinguished from all other woody plants in having this combination of features: stems not thorny, leaves alternate with three leaflets, and the middle leaflet on a much longer stalk than the others.

Black Locust, Robinia pseudoacacia L. Most cultivated trees mind their manners and stay put where planted, but the black locust has spread far beyond its natural range. Native to the Appalachian and Ozark highlands, it now grows wild across most of the Midwest, forming thickets or small groves along the edge of woods. In Iowa it is especially common in the south, where its showy white blossoms are a conspicuous feature of the landscape in late spring. Black locust is not much planted today, but one can find older trees in many Iowa communities. Its flowers are its main virtue, although its rugged bark and picturesque branching are interesting in winter. Its limitations are more numerous: spiny twigs, profuse suckering, no real autumn color, and susceptibility to problem insects. The worse pests are the locust leaf miner, which may skeletonize the foliage of entire trees, and the locust borer, which can deform or even kill trees by burrowing in the wood. As is so often true with trees, vigorously growing individuals are the most resistant. Though weedy and aggressive, black locust does have its uses. It is especially desirable for reclaiming strip-mined or eroded land, as it tolerates dry, sterile, acid conditions and holds the soil from washing away with its wide-spreading root system. It also improves the nutrient content of the soil through the action of nitrogen-fixing bacteria in nodules on its roots. Borers are more of a problem on poor sites, but the trees sprout extensively from the roots when the tops are killed. The seeds are eaten to a limited extent by quail and squirrels. The locust’s wood resembles that of Osage orange and is similarly hard, heavy, strong, and resistant to decay, with minimal shrinkage and swelling. It

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364 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s also has a high fuel value. Because of these special qualities, locust is useful for fence posts, mine timbers, insulator pins, and firewood.

Willows, Salix L. Black Willow, S. nigra Marsh. Peachleaf Willow, S. amygdaloides Anderss. White Willow, S. alba L. Crack Willow, S. fragilis L. Sandbar Willow, S. interior Rowlee   (S. exigua Nutt. ssp. interior [Rowlee] Cronq.) Missouri River Willow, S. eriocephala Michx. (S. rigida Muhl.) Pussy Willow, S. discolor Muhl. Shining Willow, S. lucida Muhl. Bebb Willow, S. bebbiana Sarg. Prairie Willow, S. humilis Marsh. Meadow Willow, S. petiolaris Smith Sage Willow, S. candida Fluegge ex Willd. Bog Willow, S. pedicellaris Pursh Silky Willow, S. sericea Marsh. Willows are to the lowlands what oaks are to the uplands. It would be difficult to find a watercourse in Iowa, whether tiny creek or major river, that did not have at least one species of willow growing along its shore. In low-lying areas, willows are often the dominant vegetation. Twelve willows are native to Iowa, and several others have been introduced for landscaping. Most of the native species are shrubs or at best small trees. Some are very rare, occurring in only a few bogs, marshes, or prairie remnants in eastern or northern Iowa. At least two of the introduced species have escaped from cultivation locally and can be found growing side by side with the natives. Our common willows are easily recognized by their narrow, finely toothed leaves, but within the genus as a whole there is a diversity of leaf characteristics. A more consistent feature is the single-scaled buds, which are arranged alternately and often tightly appressed to the twig. The twigs themselves are typically long and slender and sometimes brightly colored, a further aid in identification.

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While recognizing a tree as a willow is usually easy, identifying species is often challenging, even for botanists. Typical plants of each species are distinctive enough, but species can be quite variable and often hybridize with one another, producing plants with intermediate characteristics. Flowers are often needed to confirm an identification, and these of course are ephemeral, with the male and female flowers on separate trees. Willow flowers bloom during spring or early summer in dense, elongate clusters called catkins. The tiny blossoms lack petals and are easily overlooked, although the bright yellow stamens of male flowers are quite attractive when examined closely. In structure, the flowers are very simple. Staminate flowers consist of two to seven stamens, one or two reddish basal glands, and a subtending bract. Pistillate flowers are composed of a single flask-shaped pistil, one or two glands, and a bract. The tiny, short-lived seeds mature quickly. Extremely light in weight and equipped with long, silky hairs, they are dispersed by wind and water. Fresh deposits of silt and sand left by receding spring floodwaters provide an ideal seedbed and are rapidly colonized by seedlings of these sun-loving, fast-growing trees. Willows may propagate themselves in another interesting way that has nothing to do with flowers and seeds. The twigs of some species break easily at the base and, if stuck in soil, they root readily. When broken by floods or storms the twigs float downstream, and if they lodge in a deposit of sand or silt, a new tree may grow. Willows have little commercial importance because most species are small, and their wood is less valuable than that of other trees. They do, however, play an important role in nature by protecting stream banks from erosion and providing shelter, food, and nesting cover for birds and mammals. When harvested, the wood is used for lumber, veneer, pulp, toys, novelties, and carved items. Willows host their share of pests and diseases, including cankers, borers, and galls. One of the more interesting insects is a midge, or tiny fly, that inserts its eggs into the expanding buds in spring. Each parasitized bud then develops into a gall resembling a small pine cone. A grublike larva inhabits each gall during the summer, fall, and winter, emerging as an adult the following spring.

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Native and Naturalized Willows The largest of our native species are the black and peachleaf willows, which can grow 30 to 60 feet tall. Both can be found in floodplains, on stream banks, along lakeshores, and in low-lying meadows throughout most of the state. Black willow is probably the better known, but peachleaf is more prevalent to the northwest and is the common native willow of the natural lakes region. Both are often multistemmed and, when growing along rivers and lakes, lean far out over the water. The two are closely related botanically, differing from other willows in their more numerous stamens and in having bud scales with overlapping instead of fused margins. Two other large willows grow wild in Iowa, although neither is native. Crack willow and white willow were introduced from Eurasia and have escaped from cultivation, joining the black and peachleaf willows along rivers, lakes, and streams. The two species frequently hybridize, producing trees (S. ×rubens Schrank) with intermediate characteristics. They can be distinguished from black and peachleaf willows by their stouter twigs, larger buds, darker and more leathery leaves, and often glandular petioles. Sandbar willow is our most abundant and widely distributed willow, easily identified by its distinctive leaves, pole-like stems, thicket-forming habit, and tendency to bloom well into summer. It most commonly grows along rivers and streams but can be found in a variety of wet places including ditches, low-lying prairies, shores of lakes and marshes, and even the edges of woods. Though typically 5 or six 6 feet tall, it can reach 25 feet. Though not important commercially, sandbar willow is invaluable in erosion control and wildlife conservation. It colonizes moist, bare mineral soil along rivers and streams, producing a network of dense, fibrous roots that hold the soil until larger and more valuable trees can become established. Thickets of sandbar willow also provide shelter and nesting sites for many small birds and animals and food for deer, beaver, and rabbits. Four other native willows can grow to be substantial shrubs or small trees. Missouri River willow is a highly variable species with several named varieties. Often called heart-leaved willow — though its leaves are not heart-shaped —  it inhabits low, moist places throughout the state. Pussy willow (see below) is also widely distributed. Bebb and shining willows are two very handsome willows native in the northeastern and north central parts of the state. Rounding out the list of native Salix are several shrubby species. Prairie willow, which resembles a miniature pussy willow, grows in prairie remnants

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Sandbar willow forms thickets along stream banks in Iowa.

throughout the state. Meadow willow inhabits wetlands in the east and north central parts of Iowa. Sage willow, bog willow, and silky willow are rare.

Weeping Willows “Weeping willow” is a generic term for trees with long, drooping branches. Like other fast-growing trees, these tend to be short-lived, weak-wooded plants that don’t age gracefully. They also grow to be quite large — a wise thing to keep in mind when landscaping a small yard. The ideal spot for one is a large, open space along a pond or natural drainageway, where it will have plenty of room to spread and its habit of dropping twigs won’t be a problem. The nomenclature of the weeping willows is very confused and different types may be sold under the same name. A few of the more common ones are described below. The best known of the weeping willows is Salix babylonica L. According to Santamour and McArdle (1988), all the Babylon willows planted in the United States are female and probably represent the same clone, for which they have

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368 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s proposed the cultivar name ‘Babylon.’ These trees are not reliably hardy in the northern United States and have been crossed with the crack willow and white willow to produce hybrids that will tolerate our harsh winters. Salix ×sepulcralis Simonkai is the botanical name for crosses between the Babylon and white willows, which can vary considerably in habit. The most popular form is the golden weeping willow, often sold under the names Tristis and Niobe, a hardy tree with long, pendulous branches and bright yellow twigs. Crosses between the Babylon and crack willows are named Salix ×blanda Anderss. Individual clones have dull green or brown branches and are often sold under the names Wisconsin or Niobe. Thurlow, with lustrous brown branches, is of unknown origin but is thought by some botanists to belong to this group. Corkscrew willow (S. matsudana Koidz. ‘Tortuosa’) is another ornamental willow that is sometimes cultivated in Iowa. This medium-size tree is named for its peculiar twigs, which twist spirally in the manner of a corkscrew. It was introduced from northeastern Asia.

Pussy Willows “Pussy willow” is another general term, referring in this case to plants with a distinctive method of flowering. The catkins of these willows develop directly from overwintering buds in spring, beginning with a brief “pussy” stage in which they are short, soft, and fuzzy. As in other willows, the male and female catkins are borne on separate plants. The female catkins are gray-green and rather unassuming, but the male catkins are very colorful with their bright yellow stamens. Our native pussy willow occurs in a wide variety of wet habitats, including marshes, bogs, low-lying prairies and meadows, springy wooded slopes, and soggy ground along streams. Several Eurasian willows have larger and more attractive catkins and account for most of the cultivated plants in Iowa. All grow to be very large shrubs, so it is best to give them ample room and prune them hard and regularly. Pruning also promotes vigorous growth and larger “pussies.”

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Elderberries, Sambucus L. Common Elderberry, S. canadensis L. Red Elderberry, S. pubens Michx. [S. racemosa ssp. pubens (Michx.) House] The elderberries, or elders as they are also called, are tall shrubs with ashlike leaves, pithy stems, and small colorful fruits. Two species are native in Iowa. Common elderberry grows throughout the state on stream banks, in road ditches, in fencerows, and along the edges of moist woods, often forming thickets. Large, compact clusters of tiny white flowers bloom in early to midsummer and are followed by small, juicy, dark purple fruits. These are eaten by many kinds of birds and used by people to make pies, jellies, and wines. Adaptable and easy to grow, the elderberry is a good choice for conservation plantings and naturalistic landscaping. Red elderberry is similar but has brown instead of white pith, springblooming flowers in tall panicle-like clusters, and red fruits. It is more exacting in its habits and has a limited distribution in Iowa, growing only on moist wooded slopes in the northeastern corner of the state.

Sassafras, Sassafras albidum (Nutt.) Nees. This unusual tree is common throughout the eastern United States, ranging as far west as Michigan, Illinois, Missouri, Oklahoma, and Texas. Wild trees in Iowa are limited to a single location in Lee County, growing in and near an abandoned farmstead where they may have been introduced. Sassafras is usually a small tree but can attain a height of 60 feet or more when grown on moist, fertile soils. With picturesque branching and beautiful autumn color, it is desirable for naturalistic plantings in southeastern Iowa, in situations where its suckering will not be a nuisance. Oil of sassafras, an aromatic substance distilled from the root bark of the tree, has been used for flavoring root beer, candy, medicine, tea, and spring tonics. The durable wood is used for fence posts and occasionally for small boats.

European Mountain-ash,

Sorbus aucuparia L. [Pyrus aucuparia (L.) Gaertn.] Admired for its colorful fruits and dark green foliage, this attractive small tree is planted throughout Iowa. Birds appreciate its fruits too, but for a much dif-

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370 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s ferent reason than we do. Waxwings especially love to eat them, and when the birds depart the seeds go with them. Seedlings sometimes follow where the birds have stopped to rest. Unfortunately, mountain-ash tends to be short-lived in cultivation, often succumbing just when it reaches its prime as a landscape specimen. Like the birch, it is native to places where summers are cooler than Iowa and the soils often better drained. Our different climate and soils eventually stress the trees, increasing their susceptibility to insects and diseases. Sunscald to their thin bark, followed by cankers on the injured tissue, is a common problem that leads to the decline and eventual death of trees. Appropriate siting, proper planting, and good cultural practices may help prolong their life. Despite its name, the mountain-ash is not an ash at all but a relative of the apple, crabapples, and pears. Similar species grow in other parts of the northern hemisphere, including two in the northeastern United States and Canada: American mountain-ash, S. americana Marsh., and showy mountain-ash, S. decora (Sarg.) Schneid. These differ from the European species in having their bud scales and the lower surfaces of their leaves hairless or nearly so. They range into southwestern Wisconsin and might be expected in northeastern Iowa too, although there are no confirmed reports of their occurrence there.

Bladdernut, Staphylea trifolia L. Bladdernut is a tall, colonial shrub that is native on moist wooded slopes in eastern, central, and southern Iowa. Though not highly ornamental, it has small white flowers, attractive striped bark, and interesting bladderlike seed pods that persist through winter. Where its suckering habit is not a problem, it is useful for naturalistic landscaping.

Lilacs, Syringa L. Common Lilac, S. vulgaris L. Japanese Tree Lilac, S. reticulata (Blume) Hara. Few shrubs are more beloved than the lilacs. Our most familiar species is the common lilac from Europe, which has been cultivated for centuries. Among the largest, sturdiest, and longest-lived shrubs, it may persist in abandoned farmsteads and around old homes long after the original inhabitants have

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In early summer, the Japanese tree lilac produces conspicuous clusters of small white, strongly scented flowers.

gone. Other species have been introduced from Europe and Asia, and through selection and hybridization, hundreds of cultivars have been produced. Flower color ranges from white to dark purple. Some lilacs are small to medium-size trees, including the Japanese tree lilac, which grows 20 to 30 feet tall with an oval to rounded crown. It is hardy throughout Iowa and sometimes planted for its cherrylike bark, picturesque branching, and showy white flowers. The blossoms appear in early summer, much later than the shrubby lilacs, and produce an unusual fragrance that some people find unpleasant. Though often trouble-free, lilacs are not immune from problems. Japanese tree lilac is susceptible to a leaf-spot disease that may cause the leaves to fall early. Shrubby lilacs are sometimes infected with phytoplasma, a systemic disease spread by leafhoppers. Symptoms include reduced vigor, stunting, chlorosis, dense twiggy growths called witches’ brooms, and a second period of blooming in the fall. There is no cure, and infected plants should be removed.

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Basswoods and Lindens, Tilia L. American Basswood, T. americana L. Littleleaf Linden, T. cordata Mill. The names basswood and linden are interchangeable, different names for the same group of trees. Whatever you choose to call them, you can recognize them easily by their rounded, toothed leaves and two-scaled, sometimes bright red buds. Lindens’ flowers and fruits occur in small clusters and are nothing unusual, but their stalks bear a strange structure that resembles a small, narrow leaf. Because these are much lighter in color than the foliage, they stand out in summer. The flowers bloom rather late for a tree, from late June into July. Small but very fragrant, they are more often smelled than seen. The fruits that follow are hard, brown, and about the size of a pea. Our American species are usually called basswoods. Several species grow wild in the eastern United States, none in the West. Native Americans used their tough, fibrous inner bark, or bast, for making cords, thongs, and ropes, so the pioneers dubbed them bastwoods. Eventually the letter “t” was dropped, giving rise to the name we use today. Only one is native to Iowa, the American basswood. It is a common and often dominant tree in moist upland woods, especially on sheltered, northand east-facing slopes in stream valleys. Hard maples, red oak, and bitternut hickory are frequent companions. More so than most trees, basswood sprouts readily from the base. Trees in the woods are often multiple-stemmed, with trunks of different ages. When an older trunk eventually dies, younger ones take its place. In this way trees can survive for many years, one set of trunks replacing another. Basswood is a favorite tree of both honeybees and their keepers. Bees adore the flowers, and the nectar gives a distinctive taste to the resulting honey. Old trees in the woods are apt to be hollow and, when wild bees were more common, provided homes for them. The wood is light, soft, and easily worked and, when it contacts food, imparts no taste or odor. These qualities make it ideal for the frames of honeycombs and other apiary supplies. It is also a favorite wood for carving. Lindens are handsome trees with symmetrical shapes and attractive leaves. If you spend most of your time in town, you are most likely to see the littleleaf

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American basswood can be easily recognized in the woods as it often produces multiple trunks of different ages.

linden, which was introduced from Europe. Hardy and adaptable, it will grow in many soil types and is tolerant of urban conditions. As its name suggests, its leaves are smaller than those of the basswood. It grows at a moderate rate, developing a dense, pyramidal crown that becomes broader with age. Mature trees are usually 40 to 50 feet tall, sometimes more. Several cultivars are available. Basswood is less commonly planted, at least in its wild form. It grows quickly and can become quite large, 70 to 80 feet or more. The cultivar ‘Redmond’ is sold by nurseries. Most other lindens have very large leaves, similar to those of basswood. In some the leaves are strongly whitened below, which makes them very ornamental. These include the white basswood (T. heterophylla Vent.) from the southeastern United States and the silver linden (T. tomentosa Moench) from southeastern Europe, both of which are planted in Iowa.

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Littleleaf linden has an attractive symmetrical crown.

Lindens are usually trouble-free, but the smooth, thin bark of younger trees is sometimes damaged by sunscald or cracking during winter. Borers and various leaf-feeding insects can also become a problem.

Elms, Ulmus L. American Elm, U. americana L. Slippery Elm, U. rubra Muhl. Rock Elm, U. thomasii Sarg. Siberian Elm, U. pumila L. Chinese or Lacebark Elm, U. parvifolia Jacq. Oaks are known for their acorns, maples for their fall color, and elms, unfortunately, for a disease. Because of that disease, younger Iowans may never appreciate how common elms were, how beautiful they were, and how much they

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were favored as shade trees. Their demise ranks among the saddest chapters in America’s botanical history. The culprit is Dutch elm disease, originally from Asia but accidentally introduced to America from Europe. It is caused by a fungus, spread overland by elm bark beetles and in close quarters by root grafts between trees. Though most large elms are now gone, the disease is still here and always will be, killing trees as they grow large enough to attract the beetles. Since infected elms cannot be cured, prevention is the only option. Prompt removal of diseased and dead trees is essential, and where elms are growing close together, trenching to destroy root grafts between trees is recommended. Individual trees can be injected with a systemic fungicide. While greatly reduced in numbers, our native elms are still with us. They are prolific seeders and new trees continually appear in forest edges, waste places, and the woodland understory. Three species are native here. The best known is the American elm, once the most popular shade and street tree in America. Vigorous, adaptable, and easy to grow, it was beloved for its handsome foliage and graceful, vase-shaped crown. It was also common in nature, especially in floodplain forests. While a few large trees remain  — possibly resistant to disease but more likely just lucky — streets lined with elms are a thing of the past. Slippery elm was not much planted as a shade tree, but large trees were common in the wild. Its rough leaves make it seem oddly named, but it is another part of the tree — its inner bark — that gave it its name. This has soothing properties and was once widely used as a wound dressing, poultice, and sore throat remedy. The species is also called red elm because its heartwood has a reddish cast. The third species is the rock elm, which was always less common than the others, even before European American settlement. Today it is rare, growing near streams and at the bases of moist wooded slopes or, less commonly, on rocky slopes and limestone bluffs. All three are valued for their hard, heavy, strong, and tough wood, which has interlocked grain and is thus difficult to split. Important uses include veneer, barrel staves, hockey sticks, and furniture, especially bent parts such as rockers and arms. Rock elm was once widely used for iceboxes, washing machines, and kitchen furniture because it is so strong and easily cleaned. It was also the preferred material for the hubs and spokes of automobiles during the early days of the industry.

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Before the epidemic of Dutch elm disease, beautiful large elms like this were a common sight in Iowa.

If you encounter a large, healthy elm in Iowa today, chances are good that it is the introduced Siberian elm or a hybrid between it and the slippery elm. Though less attractive than the American elm, these are tough, adaptable trees that are resistant to Dutch elm disease. Unfortunately, Siberian elm does not age gracefully, and like most other fast-growing trees, it has weak, brittle wood that breaks easily in storms. It is also subject to leaf-eating insects, has no appreciable autumn color, and is very weedy. Siberian elm is often called Chinese elm, a name more properly applied to another species of tree. Its foliage resembles that of Siberian elm, but its flowers and fruits appear in autumn instead of spring. Its distinctive bark consists of irregularly shaped scales of orange, brown, and gray-green that fit together like the pieces of a jigsaw puzzle, giving it another common name, lacebark elm. Chinese elm is not much planted in Iowa, but it is a desirable mediumsize shade tree where hardy in the southern, eastern, and central parts of the state. Also promising are various hybrid elms that were developed from diseaseresistant Asian species, including several by George Ware at the Morton Ar-

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boretum. The best known is the Accolade elm (cultivar ‘Morton’), which is similar to the American elm in foliage and form. Most elms, native and introduced, are susceptible to a peculiar stem disease called wetwood. It is seldom fatal but can cause a chronic decline in the health of infected trees. It is caused by a bacterium that invades and ferments the sap in the trunk and larger branches. The gases resulting from this fermentation accumulate under pressure, causing the sap to exude or flux through wounds or cracks and run down the side of the tree. The fluxing sap is colorless, but when it dries it leaves a pale-colored encrustation on the bark.

Viburnums, Viburnum L. Nannyberry, V. lentago L. Downy Arrowwood, V. rafinesquianum Schultes Kentucky Viburnum, V. molle Michx. Southern Arrowwood, V. dentatum L. American Highbush Cranberry, V. trilobum Marsh. Wayfaring Tree, V. lantana L. Blackhaw, V. prunifolium L. The genus Viburnum is perhaps the largest, most diverse, and most useful group of shrubs for landscaping. Reflecting this diversity, its species have many common names: arrowwood, blackhaw, nannyberry, wayfaring tree, highbush cranberry. Despite their differences, all can be recognized by their opposite, simple, toothed leaves. Most are large shrubs, but a few can become small trees. Viburnums are admired for their foliage, flowers, fruits, and fall color. The fruits, which are usually borne in showy clusters, appear berrylike but have a single large seed inside. Dark blue is the normal color, but in some species the color changes as the fruits ripen, and a few have bright red fruits. Birds enjoy them in fall, so viburnums are good choices for wildlife plantings, too. Nannyberry is our most common viburnum, native throughout most of the state. It is also the tallest, and in the woods where it commonly grows, it is often single-stemmed and treelike in habit. Its leaves are oval to elliptic in shape with fine teeth along their margins. Nannyberry is useful for conservation plantings and naturalistic landscapes, but given its large size and suckering habit, it is not especially desirable as an ornamental.

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378 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s The arrowwoods are medium-size to large shrubs of upland woods and edges. As a group they are easily recognized by their roundish, coarsely toothed leaves, but their taxonomy is complex and the species are not easy to sort out. Native species include the downy arrowwood, found across much of the state but more common to the east; the Kentucky viburnum, rare in southeast and southwest Iowa; and the southern arrowwood, uncommon in the southwest part of the state. The highbush cranberries have bright red fruits that persist on the branches and remain colorful all winter. Their leaves are lobed, resembling those of maples. The American highbush cranberry is native on moist wooded slopes in Iowa’s northeastern corner; two other Eurasian species are planted. The leatherleaf viburnums are tall shrubs with large, thick, dark green leaves that often persist into early winter. None is native to Iowa, but the wayfaring tree from Europe is frequently planted, especially its cultivar ‘Mohican.’ One other native species, the blackhaw, occurs here and there in eastern and southern Iowa. It is useful for landscaping and can be trained as a small tree.

Prickly-ash, Zanthoxylum americanum Mill. Prickly-ash is a spiny, colonial shrub growing 4 to 12 feet tall, common throughout Iowa in clearings, open woods, and wood edges in both wet and dry soils. Its individual stems are often treelike in habit if not in height. Prickly-ash is sometimes called toothache tree because its tiny fruits numb the mouth and lips when chewed, thus providing relief from toothaches. The leaves and the leathery rinds of the fruits contain tiny oil glands that produce a citruslike aroma, indicating the relationship of this species to the lemon and orange. The bark is also aromatic and was once used as a stimulant and as a home remedy for flatulence and diarrhea.

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Promising Trees for Iowa Diver sit y is the k ey to a healthy landscape. Too great a reliance on one species can lead to disaster if a new disease or insect pest appears. Iowans learned that lesson many years ago with the American elm, and it appears we may learn it once again with the green ash. Native species should always be the backbone of a community forest, but there are trees from other parts of the world that grow well here and add variety to our landscapes. A few of these, such as the blue spruce and Norway maple, have been so widely planted that they are perhaps too familiar. Others, such as the Austrian and Scots pines, were much planted in the past but have proved susceptible to diseases or insects. Many other fine trees, however, are greatly underutilized. In today’s smaller urban spaces, there is a need for smaller trees. Unfortunately, Iowa has few native trees that remain modest in size and are also useful for landscaping. There are some, to be sure — redbud, serviceberry, and ironwood among them — but there is a need for more variety than our natives provide. It is in this size range, then, where introduced species can be especially helpful. To find useful new trees, Iowa’s arboretums are testing species from other parts of the world. Desired traits include tolerance of winter cold, adaptability to varied soil types, resistance to disease and insects, and year-round beauty. It is also essential that these new trees mind their manners and not become weeds. As time goes on, we will know more about which new species are best suited to Iowa. In the meantime, a few are promising enough that we can recommend them for planting. For the homeowner who likes something unusual, these fine trees may fit the bill: Paper-bark Maple, Acer griseum (Franchet) Pax Three-flower Maple, Acer triflorum Komarov Nikko Maple, Acer maximowiczianum Miquel (A. nikoense Maxim.) Korean Maple, Acer pseudosieboldianum Komarov Miyabe Maple, Acer miyabei Maxim

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380 n a t u r a l h i s t o r y a n d u s e s o f i o w a ’ s t r e e s Purpleblow Maple, Acer truncatum Bunge Japanese Horsechestnut, Aesculus turbinata Bl. Red Buckeye, Aesculus pavia L. Turkish Tree Hazel, Corylus colurna L. Ussurian Pear, Pyrus ussuriensis Maxim. Yellowwood, Cladrastis kentukea (Dum.-Cours.)    Rudd [C. lutea (Michx. f) K. Koch] Amur Maackia, Maackia amurensis Rupr. Limber Pine, Pinus flexilis James Swiss Stone Pine, Pinus cembra L. Lacebark Pine, Pinus bungeana Zucc. Serbian Spruce, Picea omorika (Pancic) Purkyne. Among small trees, some of the best candidates are maples. Particularly promising is a group from eastern Asia called the trifoliate maples because their leaves are divided into threes. These are the paper-bark maple, with striking copper-colored bark; three-flower maple, with mottled orange, beige, and gray bark; and Nikko maple, with smooth gray bark. All have good fall color, although this may vary from place to place and tree to tree. Three-flower maple turns golden-yellow to orange, while paper-bark and Nikko maples have pinkish to purple fall leaves. Three-flower maple is the hardiest of the three, suitable for planting throughout Iowa. Other Asian species have the more typical maple-shaped leaf. Korean maple resembles the popular Japanese maple but is more cold-tolerant. In autumn its leaves are often a mix of colors: yellow, orange, and red. Like the trifoliate maples, it is a tree of the woodland understory and is best grown in a moist, well-drained site with protection from afternoon sun. Two other nice maples have yellow fall color. Purpleblow maple from northern China grows 20 to 25 feet tall and is easily recognized by its star-shaped leaves. Miyabe maple, a handsome tree from Hokkaido, Japan, grows larger and is a nice alternative to the Norway maple. Its cultivar ‘Morton’ (trade name State Street) reaches 60 feet in height. The genus Aesculus also offers some promising species. The Japanese horsechestnut is a medium-size to moderately large tree, similar to the common horsechestnut but more resistant to disease. The red buckeye is a small tree with bright red spring flowers, native to the southeastern United States. Both could be tried in the eastern and central parts of Iowa.

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Most hazels are shrubby, but the Turkish tree hazel is a beautiful mediumsize to moderately large tree that is adapted to urban conditions. Though not colorful in autumn, its foliage remains a handsome dark green throughout the summer. It seldom produces nuts in the Midwest, perhaps because of cold damage to its flower buds. The Ussurian pear from northeast Asia grows 25 to 50 feet tall and is very hardy, suitable for planting throughout Iowa. Its white flowers make a very nice display in spring and, if pollinated by another pear, are followed by roundish fruits about 1.5 inches in diameter. The cultivar ‘MorDak’ (trade name Prairie Gem) was selected for its good ornamental qualities. There are many Chinese selections with edible fruit. The legume family offers two attractive trees of modest size, both very hardy. Though related to the locusts, their leaflets are much larger. Both produce small white flowers in summer. Yellowwood is a small to medium-size tree with smooth gray bark, native to the eastern United States. It branches low to the ground, producing a vaseshaped to rounded crown. The crotches tend to be narrow, so good pruning is needed when the trees are young to minimize the chance of splitting as they mature. Amur maackia is a smaller tree from northeast Asia, growing 20 to 30 feet tall. Similar to the yellowwood in leaf, its bark is a smooth, shiny brown. Its flowers are less showy, but the maackia offers something else of interest —  handsome silver-gray expanding leaves. Among the conifers, several pines show promise for planting in Iowa. Limber pine, which is native to the Rocky Mountains, is similar to white pine but has stouter twigs and heavier, thicker-scaled cones. Swiss stone pine is a beautiful, compact tree with a narrowly pyramidal crown, introduced from the mountains of central Europe. China’s lacebark pine is often multiple-stemmed, which sets off its attractive multicolored bark. All three are slow-growing, medium-size trees, maturing at heights of 30 to 50 feet. Limber and Swiss stone pines are hardy throughout Iowa, lacebark pine in the southern portion. Spruces grow well in Iowa, so one would expect to see more than the three species commonly grown. Several are being tested at Iowa’s arboretums. The Serbian spruce is perhaps the most striking, with graceful branches that curve upward at the ends, showing off the white lower surface of its leaves. Though cold-hardy, this tree may be injured in winter when grown in open, exposed locations.

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part thr ee

Growing Trees in Iowa

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Tr ees a dd beaut y a nd va lue to a property, but a poorly placed or selected tree can become a liability rather than an asset. How do you determine what kind of trees to plant? And how should you care for your trees as they grow and mature? The recommendations in this section can serve as a general guide, but be sure to consult those who are experienced in your locale. Arborists, nurseries, garden centers, Trees Forever, the Iowa Cooperative Extension Service, and the Iowa Department of Natural Resources can all be helpful.

Selecting Trees Trees differ in their size, growth rates, and suitability for different uses, so it is important to make your selections thoughtfully. Following are some general guidelines and recommendations. Before planting a tree, imagine how tall and wide it will eventually grow. Will it one day interfere with nearby buildings, utility wires, or other trees? If so, choose another kind of tree that won’t grow so large. Know your trees’ needs and tolerances. Does it require full sun to be healthy? Is it adapted to the climate where you live? Will it tolerate the clayey soil in your yard? For answers to questions like these, consider where trees grow in nature. Bottomland species are adapted to an environment that can change suddenly and dramatically. The soil can vary from dry to saturated, water can stand for weeks, and sediment is dumped whenever floods occur. These trees are likely to grow well almost anywhere you plant them, including upland and urban soils. Upland trees accustomed to a more stable environment with well-aerated soils, are another matter. Though resistant to drought, they don’t do so well where drainage is poor or the site is disturbed. Two notable exceptions are the bur and chinkapin oaks, which though native to dry upland woods also grow well in bottomlands and clayey soils. Most everyone prefers a tree with rapid growth. Unfortunately, most fastgrowing trees have weaker wood that breaks more easily in storms, and they tend to be short-lived. Slow-growing species have stronger wood and greater longevity. A few trees, including the locust and sycamore, grow fairly fast yet offer reasonably strong wood and longer lives. Since the early twentieth century, many American trees been devastated

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386 g r o w i n g t r e e s i n i o w a by diseases and insects. Chestnut, elm, hemlock, beech, butternut, dogwood, and ash, among others, have been or are being eliminated from our forests and landscapes. We don’t know which tree might be next, so it’s wise to plant a variety of species. Diversity has another benefit — a more interesting landscape. Trees offer much variety in the color of their new growth and autumn leaves, the patterns of their bark, and the shapes and sizes of their fruits. Different trees also attract and support different kinds of wildlife, so the more kinds of trees you plant, the greater variety of birds and animals you’ll be able to watch and enjoy.

Trees for Different Uses Space is often limited in urban and residential areas. Fortunately, there are many good small trees for places like these, including the serviceberries, flowering crabs, hornbeam, alternate-leaf dogwood, magnolias, ironwood, Japanese tree lilac, and hardier strains of redbud. Several small maples also grow well in Iowa. Where space is not so limited, desirable trees include the maples, lindens, ginkgo, Kentucky coffee tree, hackberry, and the new cultivars of diseaseresistant elms. Oaks are also excellent choices, including the red, chinkapin, and swamp white. River birch and Ohio buckeye are useful where a somewhat smaller tree, 30 to 50 feet tall, is needed. Desirable conifers include the white and Fraser firs, European larch, several kinds of spruces, white pine, Douglas-fir, baldcypress, and arborvitae. Most of these grow quite large but, fortunately, garden-size cultivars of many species are available from larger garden centers and specialty nurseries. When sited correctly, most native trees are suitable for conservation plantings in Iowa. Exceptions include the elms, which are susceptible to Dutch elm disease, and the ashes, which are susceptible to the emerald ash borer. Trees that are especially valuable for timber and wildlife include the oaks, hickories, maples, black walnut, and black cherry. State and private foresters can advise on the best trees for your property and explain the various cost-share programs that are available. To find someone to help you, go to the Iowa Department of Natural Resources website at http://www.iowadnr.gov, click State Forests/Forestry, and look under Landowner Assistance. Coniferous trees such as pines, spruces, and firs are preferred for wind-

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Where the soil is suitably drained, conifers are the preferred trees for windbreaks in Iowa.

breaks in Iowa, because their dense evergreen foliage provides the best protection from wind. Most conifers do not thrive in wet or high pH soils, however, and in such settings deciduous trees must be used. For assistance in planning a windbreak, go to the Iowa State University Forestry Extension website at http://www.forestry.iastate.edu, click All Publications, and select brochures PM1716 and PM1717. The table on page 388 lists trees recommended for shade and landscaping and for conservation and restoration. See pages 379 to 381 for some uncommon trees that are desirable for planting in Iowa.

Autumn Colors The turning of the leaves in autumn is an annual event that draws thousands of spectators, especially in the rugged northeastern corner of Iowa where abundant forest and a diversity of tree species make a striking display. The timing and intensity of the colors vary from year to year, depending on weather, but the display is usually best in early to mid October. The coloring and subsequent falling of the leaves result from a series of

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Trees for Shade and Landscaping Coniferous

Small Broadleaf

Eastern white pine

Flowering crabapples

Red oak

Norway spruce

Serviceberries

Chinkapin oak

White spruce

Redbud

Swamp white oak

Blue spruce

American hornbeam

Sugar maple

White (concolor) fir

Ironwood

Black maple

Douglas-fir

Japanese tree lilac

Kentucky coffee tree

European larch

Magnolias

Honey locust

Baldcypress

Alternate-leaf dogwood

Ginkgo

Arborvitae

Medium to Large Broadleaf

Lindens (basswoods) Sycamore Hybrid elms Hackberry River birch

Trees for Reforestation

Ohio buckeye

Well-Drained Soils

Poorly Drained Soils

Sandy or Barren Areas

Eastern white pine

Cottonwood

Jack pine

Red pine

Silver maple

Virginia pine

White oak

Hackberry

Eastern redcedar

Red oak

Sycamore

Osage orange

Chinkapin oak

Swamp white oak

Black oak

Black oak

Pin oak

Hill’s oak

Black walnut

Kentucky coffee tree

Hickories

River birch

Black cherry

Black willow

Sugar maple

Peachleaf willow

Black maple Kentucky coffee tree American basswood Aspens Note: Species are not necessarily suited to all soils and locations. For more on their qualities and limitations, see part 2.

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Y Autumn colors: (left to right, first row) American elm, quaking aspen, ginkgo; (left to right, second row) Amur maple, bigtooth aspen, downy serviceberry; (left to right, third row) callery pear, burning bush, red-osier dogwood; (left to right, fourth row) nannyberry, arrowwood viburnum, highbush cranberry

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390 g r o w i n g t r e e s i n i o w a chemical changes that occur in the leaves during late summer and early autumn. These changes are initiated by the steady increase in the length of the nights and influenced by weather. The best color occurs when conditions are clear, dry, and cool but not freezing. Contrary to popular belief, frosts actually detract from the show because they kill the leaf cells responsible for the bright colors and cause the leaves to fall early. Autumn colors result from pigments in the leaves. Some of these are produced only in autumn, while others are present throughout the summer but masked by the green pigment chlorophyll. As the production of chlorophyll slows and then ceases in autumn, and the chlorophyll already present in the leaf breaks down, the other pigments are revealed. Carotenes and their close relatives the xanthophylls are responsible for the yellows and oranges of maples, elms, ashes, hickories, aspens, locusts, and other familiar trees. These pigments are present all summer but normally hidden by chlorophyll. They also color such familiar foods as carrots, egg yolks, corn, squash, and pumpkins. Anthocyanins produce the reds and purples of maples, oaks, sumacs, dogwoods, white ash, and Virginia creeper. They are manufactured from soluble sugars in the cell sap during autumn. Their production is enhanced by cool nights that slow transport of sugars to the stem and roots, leaving more in the leaves to be converted into pigment. Anthocyanins also color beets, cran­ berries, and purple grapes. Tannins give oak leaves their brown color. Like the carotenes, they are present throughout the growing season but revealed only when other, less persistent pigments have faded. They are also found in tea, acorns, and tree bark.

Planting Trees Proper planting is the single most important step you can take to ensure the health and longevity of your trees. It is wise to take the time and effort to do the job right. Nurseries and garden centers offer several kinds of planting stock. Bareroot trees have little or no soil attached to the roots. Container-grown trees have been grown in a pot or container, while containerized trees have been dug from the nursery and placed in a container. B&B (ball-and-burlap) trees have the roots in a round ball of soil enclosed by burlap. Trees are best planted when they are dormant, not actively growing. Most

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deciduous trees can be planted in either spring or fall, but some kinds — such as oaks and magnolias — are best planted in spring. Late August and September is an ideal time for pines, spruces, junipers, and most other conifers, but they can also be planted in spring if desired. To begin, dig a hole that is the same depth as the root ball of the tree and two to three times its diameter. Take care that the tree is not planted too deep — the flare at the base of the trunk should be at ground level. Carefully remove the tree from its container and place it in the hole, or if the tree is B&B, set it in the hole and remove the twine or wire and as much burlap as possible. If the roots are tightly bound or encircling the root ball, pull them out gently. Broken roots should be cut off cleanly and removed. Back-fill with the soil you dug from the hole, taking care that you don’t compress it. Water the soil well and add mulch as described below. Staking is probably not necessary if the tree is small, but a large tree (or one with a small root ball) may need additional support. If in doubt, consult the nursery or garden center that sold you the tree. When tying a tree to a stake, use nylon hosiery, sturdy twine, or cloth. If using wire, be sure to protect the trunk of the tree by enclosing the wire with a piece of rubber hose.

Maintaining Trees Trees need ongoing maintenance if they are to remain healthy and attractive. Watering, mulching, pruning, and protection from mechanical injury are especially important. Watering is the most critical practice in the maintenance of trees. Both too much and too little water can be harmful. After a tree is transplanted, it can take as long as three months for newly grown roots to absorb appreciable moisture from soil outside the root ball. In the meantime, the root ball can dry out very quickly, even though the surrounding soil is very moist. During times of intense summer heat and drought, even established trees might require additional moisture. To determine if watering is needed, probe the soil around the roots. Water thoroughly whenever the soil feels hard and dry. Mulching helps control the growth of turf grasses and weeds, which compete with the tree for water and nutrients. Mulch also creates a more natural environment at the surface of the ground that promotes root growth and development. Apply it 3 to 4 inches deep to as large an area as practical, except for a small circle immediately around the trunk.

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392 g r o w i n g t r e e s i n i o w a The best mulch is compost topped by aged wood chips, but any coarse-textured, partially composed organic material will do. Rock mulches are less beneficial and in some cases may be harmful. Avoid lime-containing rocks around pin oaks and red maples as they may increase problems of nutrient deficiencies in those species. Pruning serves to maintain a healthy, natural shape to the tree and prevent growth defects. Whenever possible, maintain a single main trunk (leader) by pruning back competing stems. Select branches that will someday form the main limbs of the tree, and remove other branches that crowd, rub, or cross them. The widest crotches are usually the strongest and least likely to split, so remove young branches that form narrow angles with the trunk. Pruning can be done almost anytime, although late winter is ideal for most broadleaf species. Maples, birches, and some other species may bleed sap if pruned then, but this does not harm the tree. In areas where oak wilt occurs, avoid pruning oaks in May and June. Most conifers do not need regular pruning. When removing a branch, cut it off as close to the trunk as possible without severing the branch bark ridge, a raised, collarlike area that serves as a natural barrier against infection. If the branch is large, prevent its bark from peeling down the tree by cutting in three steps as follows: (1) a foot or so from the trunk, make a shallow cut on the underside of the branch, (2) just outside the first cut, cut downward until the branch breaks, and (3) remove the stub. In most cases it is not necessary to apply pruning paint to the wound, but painting is appropriate if one is forced to prune at a time of year when a disease such as oak wilt may be transmitted to the tree. Protection from mechanical injury is also important. Avoid hitting trees with lawnmowers and cutting them with string trimmers. To prevent sunscald and injury by small animals during winter, cover the trunks of young broad­ leaf trees with tree wrap or plastic tree guards in late fall. Remove the wrap or guards in early spring, when the trees begin to grow for the year. Where browsing or antler-rubbing by deer is likely, cage trees with strong fencing material. Protect the roots of your trees by limiting disturbance of the soil around them. The fine feeder roots of trees are shallower than many people realize and are easily damaged by digging, trenching, filling, grade changes, stock­ piling soil, and operating heavy equipment. Remember that the roots of trees extend at least as far as the branches and often farther. Healthy, vigorously growing trees do not require regular fertilization. How-

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ever, if a tree shows signs of a nutrient deficiency, such as yellowish (chlorotic) foliage, fertilization may be necessary or helpful. Before starting a fertilization program, test the soil to determine if any nutrient is deficient. Contact the Iowa State University Cooperative Extension Service for information and assistance.

Diseases and Insects Diseases and insects sometimes injure trees. Many are not life-threatening, so be sure to diagnose the problem before you become alarmed. In many cases, no treatment will be necessary. As is so often true, an ounce of prevention is worth a pound of cure. Where a particular disease or pest is known to be troublesome, do not plant susceptible tree species. For example, avoid white-barked birches where the bronze birch borer is a problem, and do not plant pin oaks where the soil is alkaline. Where oak wilt occurs, do not prune oaks early in the growing season. Disease and insect problems are most common on trees stressed by drought, injury, transplant shock, or old age. Whenever possible, minimize stress on your trees by protecting them from injury and by using proper planting and cultural techniques. When treatment with a pesticide is necessary, be sure to use a product that is registered for the particular disease or insect that is present. Apply the pesticide carefully according to label instructions. For current recommendations on suitable pesticides, consult your local extension office. Common diseases and insect pests include leaf spots and blotches, chewed foliage, galls, chlorosis, borers, cankers, wilt diseases, and decline. Leaf spots and blotches are mostly commonly caused by fungi and sucking insects. Although unsightly, they rarely cause serious injury, and by the time the damage is noted, it is often too late to treat anyway. Leaf problems vary in intensity from year to year, depending on the weather and other environmental conditions, so an outbreak one year will not necessarily be followed by an outbreak the next. Chewed foliage is a sign of caterpillars, sawfly larvae, or other insects. Some of these have short life cycles and disappear by the time the damage is noticed. They are not a serious concern if the damage is light or they appear late in the growing season. Treatment is warranted if they are abundant and threaten to defoliate a tree early in the growing season, as for example gypsy moths (see the discussion below).

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Fungi cause many kinds of leaf spots on Iowa’s trees. Most are not harmful.

Japanese beetles also chew the foliage of some trees, especially lindens, plums, and paper birch. As this book was written, this new pest was spreading westward in Iowa. The beetles are green and brown in color, about 3/8 inch long, and often numerous. While they do not kill trees, they can cause significant defoliation and seriously mar trees’ appearance. Pesticides will reduce the damage but need to be reapplied, as new beetles will reinfest an area after others are killed. Galls are unusual outgrowths or deformations of the stems, leaves, and flowers, usually caused by insects or mites. They are seldom a serious threat, and no treatment is necessary. Chlorosis is an abnormal loss of the green pigment chlorophyll, causing leaves to be yellow or yellow-green in color. It can have a variety of causes, including drought, but high soil pH is often involved. Pin oak, red maple, and some other species grow best in acid soils, and when they are planted in alkaline soils, they cannot absorb certain nutrients they need. Trees that are severely chlorotic are best replaced by other species, but mild cases can be treated by acidifying the soil. Mulching and watering are also advised, as they will improve the environment for root growth.

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Chlorosis is an abnormal yellowing of leaves usually caused by nutrient deficiencies or drought.

The larvae of various beetles and moths live as borers in the stems of trees, often causing significant damage.

Borers are the larvae of insects, usually beetles or moths, which tunnel inside the stems of trees. Symptoms include holes with sawdust or oozing sap, defoliation, dieback, and sometimes death. Some borers are primarily problems of weak or stressed trees, while others, such as the emerald ash borer, also attack healthy trees. Unfortunately, borers are not easily treated once they enter a tree. The best way to manage them is to avoid planting susceptible

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396 g r o w i n g t r e e s i n i o w a species. Where a susceptible species is already planted, maintain tree vigor through good cultural practices. Cankers are fungal or bacterial diseases that attack twigs, branches, or the trunks of trees. Like borers, they are often stress-related and difficult to treat. Symptoms include dead or darkened bark, craterlike depressions in the stem, defoliation, and dieback. To minimize the likelihood that your trees will be infected, follow the cultural practices described above. Wilt diseases are caused by fungi, bacteria, or nematodes that infect branches or whole trees, causing wilting, defoliation, and death. They are usually spread by insects or by root grafts between adjacent trees. There is no cure once they establish in a tree, so prevention is the best protective measure. Infected trees should be promptly removed and destroyed. Decline is a gradual loss of vigor that results in dieback and often death of a tree. Poor growth, sparse foliage, undersize leaves, and dead upper limbs are signs that decline is occurring. Common causes include drought, construction damage, and soil compaction around the roots, which often do not show their effects for several years. In urban and residential areas, chronic chlorosis and girdling roots can also cause decline. When good care is provided, early-stage decline can sometimes be arrested. More often than not, however, the decline will be progressive. Borers are often attracted to declining trees and can hasten the death of those trees.

Emerging Threats to Iowa’s Trees At the time this book was written, the gypsy moth and emerald ash borer were on the verge of entering Iowa. It is probably just a matter of time before these pests spread throughout the state. Gypsy moth damages trees in its caterpillar stage, when caterpillars eat the foliage of many kinds of trees, especially oaks. The caterpillars are of concern to foresters and homeowners because they feed early in the growing season and often occur in large numbers, completely defoliating trees. Early-season defoliation is very stressful to trees, and if repeated in subsequent years this can seriously weaken them, causing decline and attracting borers. The emerald ash borer is a small green beetle. Its grublike larvae bore into the trunk and branches of ash trees, destroying the important tissue that exists immediately under the bark. When maturing and leaving the tree, the borers leave small, D-shaped holes in the bark. (Other ash borers leave round holes.)

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Emerald ash borer attacks all species of ash and usually kills the tree. Efforts are under way to slow its spread and develop controls, so if the borer is not yet a problem where you live, enjoy your ash trees and don’t remove them prematurely. The borer is often moved with infested firewood, so be careful that you don’t transport wood of unknown or suspicious origin. More information about these problems is available online. The Iowa State University Cooperative Extension Service and Iowa Department of Natural Resources are good sources. A third emerging threat is thousand cankers disease, which has killed planted black walnut trees in the western United States and was recently discovered in Tennessee. Whether this disease will spread to Iowa and kill walnuts here is not known.

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part four

Iowa’s Forests

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Iowa is not k now n as a tree-covered state, but forests have existed here for thousands of years. Iowa’s forests rank as one of our most important natural resources, providing wildlife habitat, watershed protection, timber, recreation, and natural beauty.

History of Iowa’s Forests Everywhere you go in Iowa, the climate is moist enough to support forest. If you abandon any tract of land today, it will eventually be covered with young trees. Why then was most of Iowa covered with prairie when European Americans arrived? To find the answer, we must go far back in history to a time when natural forces, rather than people, shaped the land. During the Pleistocene, great glaciers repeatedly advanced and then retreated across Iowa. These thick sheets of ice scoured out lakes and wetlands, created hills and plains, and left deposits or drift that eventually became soil. Ten thousand years ago, after the last glacier left the state, Iowa’s climate was much cooler and moister than it is today. The land then supported a coniferous forest similar to that of modern-day Canada. When the climate later became warmer and drier, the conifers migrated northward and were replaced by broadleaf trees. As the trend toward a warmer, drier climate continued, these trees gave way, in turn, to more heat- and drought-resistant prairie plants. This warm, dry period peaked about four thousand years ago and was followed by a climate again more favorable to trees. Broadleaf forest began to advance onto the prairie but was slowed by fires, set naturally by lightning and deliberately by Native Americans. Prairie plants were adapted to these fires and grew even more vigorously afterward, but most trees were not. Then as now, the weather varied from year to year. During wet years trees began to grow on the prairie, but dry weather always returned, accompanied by fire. If not killed outright during a burn, the young trees died to the ground and later resprouted from their roots. After repeated cycles of burning and regrowth, the trees’ roots formed tough, knotted clumps or grubs in the soil. Most of Iowa’s presettlement forests were confined to river valleys, being especially prevalent in southern and eastern Iowa. Small patches of forest also occurred along the larger natural lakes in the northern part of the state. Many of these presettlement forests were more open than our forests today, with widely spaced oaks and other trees. Where fires burned regularly into these

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402 i o w a ’ s f o r e s t s woods, the ground was covered with a prairielike vegetation of grasses, sedges, and wildflowers. Settlement brought many changes. Some forests disappeared as trees were cut to provide lumber, fencing material, and other goods and to clear land for farming. Prairie fires were suppressed, which also had wide-reaching effects. With no fire to stop them, the grubs were free to grow rapidly into trees, and new trees germinated from seed as well. As a result, some forests enlarged in size and many became denser, as shrubs and saplings replaced the grasses that once grew there. The settlers also planted groves of trees, creating new “forests” where only prairie had grown before. These two phenomena — the depletion of some forests and the expansion of others — have continued to the present day. Overall Iowa has experienced a net loss of forest since European American settlement, but in some places there is more woodland now than formerly. In the Loess Hills, for example, forest continues to advance on what remains of the prairie, creating a problem for those seeking to preserve our native grasslands.

The Distribution of Native Trees The diversity of native trees is not the same throughout Iowa. The number of species is greatest in eastern Iowa and gradually declines westward as one species after another reaches the end of its geographic range. For instance, eleven species of oaks and five species of hickories inhabit the forests of southeastern Iowa, but only one of each grows naturally in the northwestern corner of the state. This difference is presumably due to the colder and drier climate in western and northern Iowa and to historical factors such as the predominance of prairie there.

Forest Communities A species of tree may occur in a variety of environments, but there is a particular environment or habitat that provides optimal conditions for its growth and development, and that is where it is most commonly found. Topography and soils are especially influential in determining where trees grow because they so strongly affect moisture, temperature, exposure, and the availability of essential nutrients. If two kinds of trees have similar environmental requirements, they will

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Topography strongly influences vegetation. Note how upland and bottomland forests differ in this photo from Dolliver State Park.

regularly occur in the same habitat. Thus, cottonwoods and silver maples often grow together along streams, while oaks and hickories dominate dry upland sites. When two or more species occur together repeatedly over a large geographic area, they are referred to collectively as a community, association, or forest type. Forest communities change over time. Fast-growing, sun-loving species are the first to colonize a site, but they cannot reproduce in the shade they create and eventually give way to longer-lived, shade-tolerant species. The latter group will persist as the dominant trees until logging or some natural disturbance starts the cycle anew. Communities also change over distance because the geographical distributions of their constituent species do not exactly coincide. A species usually becomes increasingly less common as it approaches the edge of its range and is replaced by others that are better adapted to conditions there. Iowa is an excellent place to observe this phenomenon because so many species reach the limits of their ranges here.

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Upland woods are dominated by oaks and hickories in most parts of Iowa.

Forest communities, then, change over both time and space, which complicates our efforts to describe and name them. The following paragraphs describe five basic types. There are variations on each of these, and where the environment changes gradually with distance, two adjacent communities may blend. The oak-hickory community occurs on dry uplands and on south- and west-facing slopes. The dominant trees are usually one or more of the following: white oak, bur oak, black oak, Hill’s oak, chinkapin oak, and shagbark hickory. Other common trees include white ash, black cherry, quaking and bigtooth aspens, red oak, American basswood, and, in southeastern Iowa, shingle oak and mockernut hickory. Ironwood, chokecherry, and various shrubs grow in the shade of the taller trees. The oak-maple­-basswood community occurs in moist but well-drained uplands, especially on north- and east-facing slopes and terraces in the larger stream valleys. Red oak, sugar or black maple, and American basswood usually dominate, with maple decreasing and the others increasing in relative abun-

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i o w a ’ s f o r e s t s 405

dance westward. Maple drops out of the community in western Iowa and red oak in the extreme northwest. Other large trees often found in this community are white oak, shagbark and bitternut hickories, black walnut, white and black ashes, and formerly American elm. Small trees that are common locally include ironwood, American hornbeam, serviceberries, and Ohio buckeye. The bottomland hardwoods community occurs on primary floodplains and low-lying terraces along rivers and streams. The dominant species are usually one or more of the following: silver maple, green ash, hackberry, black walnut, cottonwood, and, in some places in eastern Iowa, river birch. American elm was once a conspicuous member of this community, but large trees of this species are now scarce because of Dutch elm disease. Other tall trees that are characteristic of the bottomland hardwoods are sycamore, honey locust, Kentucky coffee tree, black and peachleaf willows, bitternut and shellbark hickories, pin oak, shingle oak, swamp white oak, butternut, and black ash. The riparian community forms a narrow belt along lakeshores, stream banks, mudflats, and sandbars. Dominant trees include cottonwood, silver maple, boxelder, and various willows. Several other species from the adjacent bottomland hardwoods community may occur to a greater or lesser extent. The northern conifer-hardwoods community occurs on steep, moist, usually north-facing slopes in northeastern Iowa. This community is centered in the northern Great Lakes states, and many of its most characteristic species drop out as they approach Iowa. The trees and shrubs that do range into Iowa are often found as minor constituents of other communities instead of a community by themselves. They include white pine, balsam fir, Canada yew, paper and yellow birches, mountain maple, quaking and bigtooth aspens, and black ash.

Stewardship of Iowa’s Forests Forests grow and persist without human intervention, so it is sometimes assumed that the best thing we can do is to leave them alone. To be good stewards, however, we need to monitor and actively manage our woodlands, even if our main goal is preserving biodiversity. Why is this so? Since Iowa was settled, people have extensively altered the landscape. Some natural forces no longer operate, and species occur here that never existed before. As a consequence, our forests are changing in ways that are not always desirable.

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Northern trees such as these white pines and balsam firs grow on steep, north-facing slopes in northeastern Iowa.

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One unfortunate change is the invasion of alien species. Common buckthorn, honeysuckles, and garlic mustard take over the woodland understory, crowding out native species and making it difficult for some trees to reproduce. The emerald ash borer, spreading west from Michigan, may eventually kill most ash trees in Iowa, while the gypsy moth is a serious threat to oaks and other trees. Grazing by livestock is also harmful to the forest. The soil becomes compacted and erodes, runoff increases, the canopy trees lose vigor and decline, the saplings needed to regenerate the forest are destroyed, and biodiversity decreases. Even deer, a native animal, can damage a forest if present in too great a number. Exclusion of fire is another change that has affected forest composition, particularly the open woods that occur in many parts of the state. Oaks need sun to reproduce, and they are able to do so only when there is open space between the trees. Unless fire occasionally occurs, the woods become choked with brush and weedy trees, which prevent the oaks from reproducing and eliminate many desirable native plants, including native perennial herbaceous plants whose dense root mats retard soil erosion and store nutrients that would otherwise be leached from the soil. Fragmentation is another concern. As Iowa’s forests have shrunk in size, they have also been broken up into smaller parcels. These smaller parcels are less able to support the ecological processes that maintain forest health, resulting in lower diversity and increased colonization by invasive species. About 90 percent of Iowa’s forests are privately owned. To encourage the conservation of Iowa’s woodlands, the Iowa General Assembly has adopted the Iowa Forest Reservation Laws (Code of Iowa, chapters 161 and 441). Under the provision of these statutes, groves and forests may be exempted from taxation if they have a minimum size of two contiguous acres and a minimum number of two hundred trees per acre. Applications can be made at your county assessor’s office. Information and assistance in managing woodlands are available from the Iowa State University Cooperative Extension Service and the Iowa Department of Natural Resources. Go online to http://www.extension.iastate.edu or http://www.iowadnr.gov.

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The Woodland Understory A healthy forest includes a diversity of native shrubs, herbs, and wildflowers in addition to trees. In many of Iowa’s forests, these native plants have been replaced by nonnative shrubs and weeds. This loss is more than cosmetic, because the invaders do not provide all the ecological benefits of the natives. Most of the weeds are annuals and biennials, lacking the dense root structure (up to four times greater) formed by the native perennials. There is some good news in this — native perennials such as hepatica, bloodroot, and wild ginger can be restored. When seeded or transplanted into woodland habitat, they expand surprisingly rapidly and displace most annual and biennial weeds. In the late 1970s, Don Farrar and his students rescued twenty species of native woodland perennials from a section of the Des Moines River that was to be flooded by the new Saylorville Dam. These were transplanted to a small woodland with no native understory. All the species survived and within ten years produced a continuous ground cover. At the time of this writing, the display of spring wildflowers in this restored woodland rivals that found in Iowa parks and preserves, and weeds are absent.

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part five

Good Places to See Trees in Iowa

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W her e ca n you go to see a variety of trees, something more than the common species that line our streets and shade our houses? Arboretums and botanical gardens are especially good places to visit because their collections are diverse and the trees are usually labeled. Other good places are state and local parks, college campuses, and even cemeteries. Following are a few sites the authors recommend. Go to the Iowa Department of Natural Resources website for more information about state parks and preserves.

Backbone State Park, Delaware County This is Iowa’s oldest state park, dedicated in 1920 for its outstanding natural and scenic qualities. More than 20 miles of hiking trails provide access to its varied terrain and habitats. Sugar maple, basswood, oaks, and white pine inhabit upland areas, including the high ridge for which the park is named. A drive through the northern section provides good views of black walnut and other bottomland trees.

Bickelhaupt Arboretum, Clinton County This small but very nice arboretum is located in the city of Clinton. Visitors can see a good variety of native and introduced trees, plus the largest collection of garden conifers in Iowa. The grounds are well maintained and the trees are labeled. Admission is free. For directions and more information, go to www.bick-arb.org.

Brenton Arboretum, Dallas County Located in the countryside near Des Moines, this arboretum occupies a beautiful rolling site with patches of restored prairie and a small lake. Trees of the same kind are planted in small groups or groves, so that visitors can see the variation among individuals. The plantings are diverse, with good collections of oaks, elms, crabapples, and Iowa natives. The trees are labeled and connected by a network of mowed walking trails. Admission is free. For directions and more information, go to www.thebrentonarboretum.org.

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Brush Creek Canyon, Fayette County This beautiful state preserve is home to a good variety of native species and forest types. The terrain is rugged, and visitors must be in good condition to appreciate the full diversity of the site.

Fort Defiance State Park, Emmet County This park occupies a scenic stream valley near the Des Moines River and features the oak-maple-basswood forest at the edge of its geographic range. A network of hiking and horseback trails connects upland, slope, and stream-valley habitats.

Iowa Arboretum, Boone County This nonprofit arboretum is located on 378 acres in rural Boone County. It is a tree lover’s delight, with a great variety of both native and cultivated trees, many of them labeled. The planted collections are diverse and include nut trees, conifers, shade trees, and ornamentals. Much of the site is wooded, with trails offering nice views of a scenic stream valley. Both the oak-hickory and oak-maple-basswood forest types are well represented. Donations are appreciated when visiting. For directions and more information, go to www.iowa arboretum.org.

Ledges State Park, Boone County This is perhaps the premier park in central Iowa, with extensive upland forest, reconstructed prairie, and a beautiful sandstone canyon. Thirteen miles of hiking trails provide access to the varied habitats and rich flora in the park, which includes all the trees native to this part of Iowa. The walk-in campground offers views of Iowa’s oldest oaks.

Pikes Peak State Park, Clayton County Pikes Peak offers spectacular views of the Mississippi River valley and is a good place to see native trees, including the rare yellow birch.

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Preparation Canyon State Park, Monona County Though damaged by a tornado in 2008, this is still a good place to enjoy the scenic landscapes of the Loess Hills and see trees native to western Iowa: bur oak, basswood, hackberry, Kentucky coffee tree, black walnut, bitternut hickory, and others.

Pilot Knob State Park, Hancock County North central Iowa is not rich in tree species, but Pilot Knob is home to one of the largest forests in that part of the state and is a good place to see the trees that are native in the area. Hill’s oak, one of Iowa’s lesser-known oaks, is common and near the edge of its geographic range there. The panoramic view from the park’s historic stone tower is another reason to visit.

Sharon Bluffs, Appanoose County This park on the Chariton River near Centerville is owned by the state of Iowa and managed by the Appanoose County Conservation Board. Two of Iowa’s most important forest types, the oak-hickory and bottomland hardwoods, are well represented in the park and easily accessed by trails. The tree flora is diverse, with an interesting population of hybrid oaks (Quercus ×bushii, see page 359) in the uplands and shellbark hickory in the bottomlands.

Shimek State Forest, Lee and Van Buren Counties This is one of several very nice forests that are owned by the state of Iowa; all are excellent places to see our native trees. Shimek occupies more than 9,000 acres near Farmington. It offers good views of oak-hickory forest and the trees that comprise it, including species that are limited to the southern part of the state. Visitors can also see bottomland hardwoods and plantations of conifers, tulip tree, and other introduced species. For more information on Shimek and other state forests, go to www.iowadnr.gov/forestry/forests.html.

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Waubonsie State Park, Fremont County Waubonsie offers good hiking, great scenery, and nice views of the trees of the southern Loess Hills, including such uncommon species as red mulberry and pawpaw.

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Glossary

achene: a small, dry, single-seeded fruit. acuminate: tapered to a slender tip. acute: pointed. alternate: occurring singly at each node on the twig. anther: a pollen-bearing sac terminating the stamen. apetalous: lacking petals. apex: tip or end. axil: the angle between the base of the petiole and the twig. bisexual (flower): having both male and female parts. blade: the broad, flattened portion of a leaf exclusive of the petiole stalk. bract: a small, leafy or chaffy structure at the base of a flower, cone scale, or other anatomical feature. branchlet: a small branch consisting of a twig and several years’ previous growth. bundle scar: a small dot or line within a leaf scar, marking the place where a vascular bundle of the leaf entered the twig. capsule: a podlike fruit with more than one internal chamber, usually splitting open along two or more seams. carpel: the female part of a flower, often united into a flask-shaped structure called the pistil with a narrow neck or style and a swollen tip or stigma. catkin: a cylindrical cluster of small, closely spaced, imperfect, and apetalous flowers, often long, drooping, and tail-like; also known as an ament. chambered (pith): consisting of thin cross walls with no tissue in between. compound (leaf): divided into two or more separate blades. corymb: a branched inflorescence with a flat or convex top; see figure 3. cultivar: a group of plants that share a feature or features that make them desirable horticulturally and are propagated in such a way that these features are maintained from one generation to the next. deciduous: falling from the tree at the end of the growing season or at some other regular time each year. diaphragmed (pith): solid with cross walls at regular intervals. dioecious: having male and female flowers on separate plants, so individual plants are either male or female. drupe: a fleshy fruit with a large, hard seed (stone) in the middle (cherry, plum, olive).

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416 g l o s s a r y elliptic: about twice as long as wide, and widest near the middle; see figure 1. entire (leaf margin): not toothed. escaped (species): growing in a wild place after its seeds were dispersed there from cultivated trees. fascicle: a bundle of needlelike leaves surrounded by a small sheath at the base. follicle: a podlike fruit with a single chamber, opening along a single seam. glabrous: lacking hairs. gland: a small dotlike or lumplike secretory structure. globose: ball-shaped. imperfect (flower): having either male or female parts but not both. indehiscent: not splitting open. inferior (ovary): having the petals at its end (compare to superior). inflorescence: flower cluster; see figure 3. introduced (species): imported into an area by people. irregular (flower): having petals of different sizes and shapes. lanceolate: several times longer than wide with the base wider than the tip; see figure 1. leaflet: an individual blade of a compound leaf. leaf scar: a small impression on a winter twig, marking the place where a leaf was attached during the previous growing season; see figure 2. legume: a beanlike fruit with a single chamber, the seeds lined up in a row, and two seams. lenticel: a pore in the bark of a twig or stem, usually dotlike or linelike in shape and sometimes much different in color than the bark. linear: long and narrow with nearly parallel sides; see figure 1. lobed: a leaf with large indentations as in maples and oaks. monoecious: having male and female flowers on the same plant. naked (bud): lacking scales. native (species): growing naturally in an area before it was settled by people and not introduced by them either deliberately or accidentally. naturalized (species): escaped from cultivation and reproducing successfully in the wild as if native. node: the portion of a twig where a leaf and bud occur. nutlet: a small, nutlike fruit.

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oblanceolate: several times longer than wide with the tip wider than the base, the opposite of lanceolate. oblong: two to three times longer than wide with nearly parallel sides; see figure 1. obovate: egg-shaped in outline with the tip wider than the base, the opposite of ovate. once-pinnately compound: pinnately compound with the rachis (stem) of the leaf not branched; see figure 1. opposite: occurring in pairs at each node (spot) on the twig, one on either side. oval: slightly longer than wide and widest near the middle; see figure 1. ovary: the usually bulbous base of the pistil containing ovules (which eventually develop into seeds). ovate: egg-shaped in outline with the base wider than the tip; see figure 1. ovoid: egg-shaped. ovoid-elongate: resembling an egg in shape but longer relative to its diameter. palmately compound (leaf): with the leaflets arranged around a common point, like the spokes of a wheel or the spread fingers of a hand; see figure 1. palmately veined: having three or five equally prominent veins originating from the point where the petiole joins the blade. panicle: a branched inflorescence whose top is not flat; see figure 3. pendant: hanging down. perfect (flower): having both male and female parts. petiole: the stalk of a leaf. pinnately compound (leaf): with the leaflets arranged along either side of a central stem, like the barbs of a feather; called twice-pinnately compound if  branched; see figure 1. pinnately veined: having a single prominent midvein with smaller veins branching from it at regular intervals. pistil: a usually flask-shaped structure occupying the center of the flower and consisting of one or more carpels. pistillate (flower): female. pith: the center core of a twig. polygamous: having both perfect and imperfect flowers on one individual plant. pome: a fleshy fruit with the seeds confined to a separate section in the middle and the remnants of the flower located on the end opposite the stem (apple, pear). pubescent: hairy. pyramidal: pyramid-shaped. raceme: an inflorescence consisting of a single, unbranched stem with stalked flowers; see figure 3. rachis: the stem of a pinnately compound leaf to which the leaflets are attached.

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418 g l o s s a r y regular (flower): with the petals of the same size and shape. samara: a dry, winged fruit with the seed at one end or in the middle (maple, ash). sepals: the outer whorl of flower parts, usually green and leafy in appearance. sessile: not stalked. simple (leaf): with a single blade, not divided into leaflets; see figure 1. sinus: the space between two leaf lobes. spike: an inflorescence consisting of a single, upright, unbranched stem with unstalked flowers; see figure 3. spines: modified, thornlike stipules occurring in pairs at each node. spur shoot: a short, stubby twig with closely spaced leaves and leaf scars. stamen: the male part of a flower, consisting of a slender stalk or filament and a pollen-bearing sac called the anther. staminate (flower): male. stigma: the tip of the pistil, usually thicker than the style. stipule: a small, leafy structure usually occurring in pairs at the base of a leaf petiole that leaves a small, linelike scar on the twig when it falls. style: the usually elongated and slender portion of the pistil immediately above the ovary. subglobose: nearly ball-shaped, slightly longer than it is wide or thick. subopposite: associated in pairs but not exactly opposite. subtended: immediately beneath. superior (ovary): having the petals at its base (compare to inferior). terminal bud: a usually much larger bud that occupies the tip of the twig. truncate: with the end leveled off as if it were cut away, not pointed or rounded. umbel: an inflorescence with multiple stems of similar length radiating from a common point, like the ribs of an umbrella; see figure 3. unisexual (flower): having either male or female parts but not both. whorled: having three or more leaves, buds, or leaf scars at each node.

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Bi bl iogr a ph y

Aikman, J. M., and C. L. Gilly. 1948. A comparison of the forest floras along the Des Moines and Missouri rivers. Proceedings of the Iowa Academy of Science 55:63–79. ———  and A. Hayden. 1938. Iowa trees in winter. Iowa State College Extension Circular 246. ———  and A. W. Smelser. 1938. The structure and environment of forest communities in central Iowa. Ecology 19:141–50. Alden, H. A. 1997. Softwoods of North America. USDA Forest Service FPL-GTR-102. Argus, G. W. 1986. The genus Salix (Salicaceae) in the southeastern United States. Systematic Botany Monographs. Vol. 9. American Society of Plant Taxonomists. Ball, C. R. 1899. The genus Salix in Iowa. Proceedings of the Iowa Academy of Science 7:141–59. ——— . 1946. More plant study: Fewer plant names. Journal of the Arnold Arboretum of Harvard University 27:373–85. Barlow, C. 2002. The Ghosts of Evolution: Nonsensical Fruit, Missing Partners, and Other Ecological Anachronisms. Basic Books, New York. Becraft, R. J. 1924. Quercitron oak and its relation to soils. Proceedings of the Iowa Academy of Science 31:129. Bode, I. T., and G. B. MacDonald. 1928. A handbook of the native trees of Iowa. Iowa State College Extension Service, Ames. Cahayla-Wynne, R., and D. C. Glenn-Lewin. 1978. The forest vegetation of the Driftless Area, northeast Iowa. American Midland Naturalist 100:307–19. Campbell, R. B. 1961. Trees of Iowa. Iowa State University Cooperative Extension Service Bulletin P21 (rev.). Carson, G. 1978. How the West was won. Natural History 87(9):84–98. Carter, J. L. 1960. The Flora of Northwestern Iowa. University Microfilms, Ann Arbor, Mich. Clark, O. R. 1926. An ecological comparison of two types of woodland. Proceedings of the Iowa Academy of Science 33:131–34. Clark, R. C. 1989. Chinkapin oak: Satisfaction for the homeowner, skulduggery for the botanist. Morton Arboretum Quarterly 25(1):10–16. Collier, H. O. J. 1963. Aspirin. Scientific American 209:97–108. Conard, H. S. 1952. The vegetation of Iowa. University of Iowa Studies in Natural History 19:1–166. Cooperrider, M. 1957. Introgressive hybridization between Quercus marilandica and Q. velutina in Iowa. American Journal of Botany 44:804–10.

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420 b i b l i o g r a p h y Cooperrider, T. S. 1958. The Flora of Clinton, Jackson, and Jones Counties, Iowa. University Microfilms, Ann Arbor, Mich. Countryman, D. W., and D. P. Kelley. 1981. Management of existing hardwood stands can be profitable for private woodland owners. Iowa State Journal of Research 56(2):119–30. Culley, T. M., and N. A. Hardiman. 2007. The beginning of a new invasive plant: A history of the ornamental callery pear in the United States. BioScience 57(11): 956–964. Davidson, R. A. 1957. The Flora of Southeastern Iowa. University Microfilms, Ann Arbor, Mich. ——— . 1961. Comparisons of the Iowa forest resource in 1832 and 1954. Iowa State Journal of Science 36:133–36. Davis, E. F. 1928. The toxic principle of Juglans nigra as identified with synthetic juglone, and its toxic effects on tomato and alfalfa plants. American Journal of Botany 15:620. Del Tredici, P. 1991. Ginkgos and people: A thousand years of interaction. Arnoldia 51(2):2–15. Desmarais, Y. 1952. Dynamics of leaf variation in the sugar maples. Brittonia 7:347–87. Dick-Peddie, W. A. 1955. Presettlement forest types in Iowa. Ph.D. dissertation, Iowa State University. Dirr, M. A. 1975. Manual of Woody Landscape Plants: Their Identification, Ornamental Characteristics, Culture, Propagation, and Uses. Stipes Publ., Champaign, Ill. Dorn, R. D. 1975. A systematic study of Salix section Cordatae in North America. Canadian Journal of Botany 53:1491–1522. ——— . 1976. A synopsis of American Salix. Canadian Journal of Botany 54:2769–89. Eilers, L. J. 1964. The Flora and Phytogeography of the Iowan Lobe of the Wisconsin Glaciation. University Microfilms, Ann Arbor, Mich. ———  and D. M. Roosa. 1994. The Vascular Plants of Iowa. University of  Iowa Press, Iowa City. Erdmann, G. G. 1966. Promising conifers for western Iowa. USDA Forest Service Research Paper NC-8. Farrar, D. R. 1997. Forest research in Iowa’s state parks — the value of natural diversity. Journal of the Iowa Academy of Science 104:39–42. ——— . 2002. Exotic and invasive woody plant species in Iowa. Journal of the Iowa Academy of Science 108:154–57. ——— , D. M. Roosa, and J. C. Prior. 1985. Iowa’s Loess Hills — a national treasure. Proceedings of the Iowa Academy of Science 92:157–58. Fay, M. J. 1951. The flora of Cedar County, Iowa. Proceedings of the Iowa Academy of Science 58:107–31.

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i n de x

Abies balsamea 80–81, 269, 406 concolor 78–79, 268–269 fraseri 81, 269 Acer ginnala 144–145, 292–293 griseum 380 maximowiczianum 380 miyabei 380 negundo 94–95, 291–292 nigrum 136–137, 287–288 palmatum 293 platanoides 138–139, 288–289 pseudosieboldianum 380 rubrum 142–143, 290–291 saccharinum 140–141, 289–290 saccharum 134–135, 286–288 spicatum 292 triflorum 380 truncatum 380 Aesculus glabra 102–103, 293–294 hippocastanum 104–105, 295 pavia 380 turbinata 380 Ailanthus altissima 124–125, 295 alders 296 Alnus 296 Amelanchier alnifolia 298 arborea 224–225, 297 humilis 298 interior 297–298 laevis 297 sanguinea 298 Amorpha fruticosa 323 apple common 331–332 crab 180–181, 218–219, 331–335 arborvitae 92–93, 282–283 ash black 100–101, 319

blue 319 green 96–97, 318–319 mountain- 120–121, 369–370 prickly- 126–127, 378 white 98–99, 319 Asimina triloba 250–251, 298 aspen bigtooth 188–189, 339–342 quaking 186–187, 339–342 baldcypress 86–87, 281 basswood 232–233, 372–374 beech, American 359–360 Betula alleghaniensis 200–201, 300–302 lutea 200–201, 300–302 nigra 196–197, 299–300 papyrifera 198–199, 300–301 pendula 302 platyphylla var. japonica 302 pumila 302 birch dwarf 302 European white 302 Japanese white 302 paper 198–199, 300–301 river 196–197, 299–300 Whitespire 302 yellow 200–201, 300–302 blackhaw 377 bladdernut 370 bluebeech 206–207, 302–303 borers 395 bronze birch 299 emerald ash 318 Zimmerman pine 279 boxelder 94–95, 291–292 buckeye Ohio 102–103, 293–294 red 380 buckthorn 238–239, 360–361 buffalo berry 317

M

Y

428 i n d e x butternut 108–109, 326 buttonbush 309 Carpinus caroliniana 206–207, 302–303 Carya cordiformis 116–117, 306 illinoensis 118–119, 306 laciniosa 112–113, 306 ovata 110–111, 304–305 tomentosa 114–115, 306 Castanea dentata 360 catalpa 254–255, 307 cedar red 90–91, 269–270 white 92–93, 282–283 Celtis occidentalis 216–217, 307–309 Cephalanthus occidentalis 309 Cercis canadensis 252–253, 309–310 cherry bird 346 black 226–227, 343–344 Canada red 346 choke 228–229, 344–346 cornelian- 312 dwarf 345 pin 345 sand 345 Shubert 346 chestnut American 360 Cladrastis kentukea 381 coffee tree Kentucky 132–133, 323–324 corktree Amur 337 Cornus 260–261, 310–312 Corylus americana 202–203, 312 colurna 381 cornuta 203, 312 cottonwood 184–185, 339–341 crabapple flowering (ornamental) 218–219, 332–335 prairie (wild) 180–181, 332 Crataegus calpodendron 315 chrysocarpa 315 coccinea 315

crus-galli 222–223, 314 disperma 315 margaretta 314 mollis 178–179, 313–314 pedicellata 315 phaenopyrum 314–315 pruinosa 315 punctata 314 succulenta 315 cucumber tree 331 cypress bald 86–87, 281 decline 396 Diospyros virginiana 315–316 dogwoods 260–261, 310–312 Douglas-fir 76–77, 279, 281 Elaeagnus angustifolia 258–259, 316–317 umbellata 317 elderberry 369 elm American 208–209, 374–375 Chinese (lacebark) 376 hybrid 376–377 red 210–211, 374–375 rock 212–213, 374–375 Siberian 214–215, 376 slippery 210–211, 374–375 Euonymus alatus 317 atropurpureus 240–241, 317 Fagus grandifolia 359–360 fertilization of trees, 392–393 fir balsam 80–81, 269, 406 Douglas- 76–77, 279, 281 Fraser 81, 269 white 78–79, 268–269 fragmentation of forests 407 Fraxinus americana 98–99, 319 nigra 100–101, 319 pennsylvanica 96–97, 318–319 quadrangulata 319

M

Y

galls 394 ginkgo 166–167, 320–321 Gleditsia triacanthos 130–131, 321–323 Gymnocladus dioicus 132–133, 323–324 gypsy moth 396 hackberry 216–217, 307–309 Hamamelis virginiana 236–237, 324 hawthorn cockspur 222–223, 314 dotted 314 downy 178–179, 313–314 fireberry 315 fleshy 315 frosted 315 Margaret’s 314 pear 315 scarlet 315 spreading 315 Washington 314–315 hazel American 202–203, 312 beaked 203, 312 Turkish tree 381 witch- 236–237, 324 hedge apple 246–247, 329–330 hemlock 82–83, 284 hickory bitternut 116–117, 306 mockernut 114–115, 306 pecan 118–119, 306 shagbark 110–111, 304–305 shellbark 112–113, 306 highbush cranberry 377 honeysuckles 262–263, 328–329 hop hornbeam 204–205, 336–337 hoptree 347 hornbeam 206–207, 302–303 horsechestnut common 104–105, 295 Japanese 380 indigo bush 323 ironwood 204–205, 336–337 Juglans cinerea 108–109, 326 nigra 106–107, 324–326, 397

i n d e x 429 juneberry. See serviceberry juniper common 270 creeping 270 Juniperus communis 270 horizontalis 270 virginiana 90–91, 269–270 Kentucky coffee tree 132–133, 323–324 larch eastern 85, 271 European 84–85, 270–271 Larix decidua 84–85, 270–271 laricina 85, 271 lilac common 370–371 Japanese tree 256–257, 370–371 linden American 232–233, 372–374 littleleaf 234–235, 372–374 Liquidambar styraciflua 170–171, 326–327 Liriodendron tulipifera 168–169, 327–328 locust black 128–129, 363–364 honey 130–131, 321–323 Lonicera 262–263, 328–329 maackia 381 Maclura pomifera 246–247, 329–330 Magnolia acuminata 331 ×soulangeana 248–249, 330–331 stellata 331 magnolia saucer 248–249, 330–331 star 331 Malus ioensis 180–181, 332 pumila 331–332 maple Amur 144–145, 292–293 black 136–137, 287–288 boxelder 94–95, 291–292 hard 286–289 Japanese 293

M

Y

430 i n d e x Korean 380 Miyabe 380 mountain 292 Nikko 380 Norway 138–139, 288–289 paperbark 380 purpleblow 380 red 142–143, 290–291 silver 140–141, 289–290 soft 289–291 sugar 134–135, 286–288 three-flower 380 May tree 346 Morus alba 174–175, 335–336 rubra 176–177, 335–336 mountain-ash 120–121, 369–370 mulberry red 176–177, 335–336 white 174–175, 335–336 mulching 391–392 musclewood 206–207, 302–303 nannyberry 242–243, 377 oak black 158–159, 356 blackjack 164–165, 359 bur 4, 146–147, 352, 354 chinkapin 150–151, 354–355 dwarf 151, 355 English 355 Hill’s 160–161, 358 northern pin 160–161, 358 overcup 355 pin 162–163, 356, 358 post 154–155, 355 red 156–157, 355–357 scarlet 358, 359 shingle 244–245, 358–359 Shumard 359 swamp white 152–153, 354–355 white 148–149, 352–354 olive autumn- 317 Russian- 258–259, 316, 317 Osage orange 246–247, 329–330 Ostrya virginiana 204–205, 336–337

pawpaw 250–251, 298 peach 346 pear Bradford 347 callery 220–221, 347–348 Ussury 381 pecan 118–119, 306 persimmon 315–316 Phellodendron amurense 337 Picea abies 70–71, 272 glauca 72–73, 272 omorika 381 pungens 74–75, 272 pine Austrian 62–63, 277, 280 jack 277 lacebark 381 limber 381 mugo 68–69, 277 Norway 60–61, 277 Ponderosa 64–65, 277 red 60–61, 277 Scots 66–67, 277 Swiss stone 381 Virginia 277 white 58–59, 275–276 Pinus banksiana 277 bungeana 381 cembra 381 flexilis 381 mugo 68–69, 277 nigra 62–63, 277, 280 ponderosa 64–65, 277 resinosa 60–61, 277 strobus 58–59, 275–276 sylvestris 66–67, 277 virginiana 277 planetree London 338 Platanus ×acerifolia 338 occidentalis 172–173, 337–338 plum American 230–231, 345–346 big-tree 346 Canada 346

M

Y

goose 346 purpleleaf 346–347 poison ivy 362–363 poplar balsam 343 Bolleana 343 hybrid 343 Lombardy 342 white 182–183, 342–343 Populus alba 182–183, 342–343 balsamifera 343 deltoides 184–185, 339–341 grandidentata 188–189, 339–342 nigra var. italica 342 tremuloides 186–187, 339–342 prickly-ash 126–127, 378 pruning 392 Prunus americana 230–231, 345–346 besseyi 345 cerasifera 346–347 hortulana 346 mexicana 346 nigra 346 padus 346 pensylvanica 345 persica 346 pumila 345 serotina 226–227, 343–344 virginiana 228–229, 344–346 Pseudotsuga menziesii 76–77, 279, 281 Ptelea trifoliata 347 Pyrus. See also Malus, Sorbus calleryana 220–221, 347–348 ussuriensis 381 Quercus alba 148–149, 352–354 bicolor 152–153, 354–355 borealis 156–157, 355–357 ×bushii 359 coccinea 358, 359 ellipsoidalis 160–161, 358 imbricaria 244–245, 358–359 lyrata 355 macrocarpa 4, 146–147, 352, 354 marilandica 164–165, 359

i n d e x 431

muhlenbergii 150–151, 354–355 palustris 162–163, 356, 358 prinoides 151, 355 robur 355 rubra 156–157, 355–357 shumardii 359 stellata 154–155, 355 velutina 158–159, 356

redbud 252–253, 309–310 redcedar 90–91, 269–270 Rhamnus 238–239, 360–361 Rhus aromatica 362 copallina 362 glabra 361–362 radicans 362–363 typhina 122–123, 361–362 Robinia pseudoacacia 128–129, 363–364 Russian-olive 258–259, 316–317 Salix alba 366 amygdaloides 192–193, 366 babylonica 367–368 bebbiana 366 ×blanda 368 candida 367 discolor 368 eriocephala 366 exigua 194–195, 366 fragilis 366 humilis 366–367 interior 194–195, 366 lucida 366 matsudana ‘Tortuosa’ 368 nigra 190–191, 366 pedicellaris 367 petiolaris 367 rigida 366 ×sepulcralis 368 sericea 367 Sambucus 369 saskatoon 298 sassafras 369 serviceberry Allegheny 297 downy 224–225, 297

M

Y

432 i n d e x inland 297–298 low 298 round-leaf 298 shadbush. See serviceberry Shepherdia argentea 317 Sorbus americana 370 aucuparia 120–121, 369–370 decora 370 spruce Black Hills 272 blue 74–75, 272 Norway 70–71, 272 Serbian 381 white 72–73, 272 Staphylea trifolia 370 sumac fragrant 362 shining 362 smooth 361–362 staghorn 122–123, 361–362 sweetgum 170–171, 326–327 sycamore 172–173, 337–338 Syringa reticulata 256–257, 370–371 vulgaris 370–371 tamarack 85, 271 Taxodium distichum 86–87, 281 Taxus 88–89, 282 thousand cankers disease 397 Thuja occidentalis 92–93, 282–283 Tilia americana 232–233, 372–374 cordata 234–235, 372–374 heterophylla 373 tomentosa 373 Toxicodendron radicans 362–363 tree-of-heaven 124–125, 295 Tsuga canadensis 82–83, 284 tulip tree 168–169, 327–328

Ulmus americana 208–209, 374–375 parvifolia 376 pumila 214–215, 376 rubra 210–211, 374–375 thomasii 212–213, 374–375 viburnum 242–243, 377–378 wahoo 240–241, 317 walnut black 106–107, 324–326, 397 wayfaring tree 377 wetwood 377 willow Bebb 366 black 190–191, 366 bog 367 corkscrew 368 crack 366 heart-leaved 366 meadow 367 Missouri River 366 peachleaf 192–193, 366 prairie 366–367 pussy 368 sage 367 sandbar 194–195, 366 shining 366 silky 367 weeping 367–368 white 366 witch-hazel 236–237, 324 yellowwood 381 yews 88–89, 282 Zanthoxylum americanum 126–127, 378

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