Urban Lichens: A Field Guide for Northeastern North America 9780300263039

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n cHEnS

A Field Guide for Northeastern North America including New York City  Chicago Toronto  Boston New Haven Philadelphia  Baltimore Washington, D.C.

Jessica L. Allen and James C. Lendemer Illustrations and Selected Photographs by Jordan R. Hoffman

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Furthermore grants in publishing, a program of the J. M. Kaplan Fund

Yale University Press books may be purchased in quantity for educational, business, or promotional use. For information, please e-mail [email protected] (U.S. office) or [email protected] (U.K. office). Designed by Patrick Barber Set in Benton Sans, Zenon, and VTC Carrie by Adrianna Sutton

The Community Foundation for Greater New Haven

Printed in the United States of America

Mohamed bin Zayed Species Conservation Fund

ISBN 978-0-300-252996 (alk. paper)

Torrey Botanical Society Copyright © 2021 by Jessica L. Allen, James C. Lendemer, and Jordan R. Hoffman. All rights reserved. This book may not be reproduced, in whole or in part, including illustrations, in any form (beyond that copying permitted by Sections 107 and 108 of the U.S. Copyright Law and except by reviewers for the public press), without written permission from the publishers.

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Library of Congress Control Number: 2020952521 A catalogue record for this book is available from the British Library. This paper meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper). 10 9 8 7 6 5 4 3 2 1

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Publication supported by a grant from The Community Foundation for Greater New Haven as part of the Urban Haven Project

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COnT Dedicated to Irwin (Ernie) Brodo and everyone who appreciates and studies urban lichens

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nTenTS One Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 The Lichen Lifestyle: Basic Biology and Identification. . . . . . . . . . . . . . . . 3 Urban Lichens. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 New York City Lichens Through Time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Why Are Lichens Affected by Air Pollution?. . . . . . . . . . . . . . . . . . . . . . . . . 12 Lichen Chic: Fashion, Finance, and Fortune . . . . . . . . . . . . . . . . . . . . . . . . 14 Lichens and Animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Hunting Lichens in Cities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Fifty Lichens in One Day: A Whirlwind Tour of New York City. . . . . . . . . . 21

Two The Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Crustose Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Foliose Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Fruticose Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 Key to the Species. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

Three Lichens of New York City: The Complete List . . . . . . . . . . . . . . . . . . . . . 134 Illustrated Glossary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 Bibliography and Further Resources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

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The inside of each lichen is full of diversity, including fungi, algae, bacteria, tiny worms, and water bears.

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uction Lichens are some of the most fascinating and widespread lifeforms on the planet. Their fundamental makeup alone inspires the imagination, as they are not one single organism but at least two. The majority of a lichen is an intensive cooperation between a fungus and an alga or a cyanobacterium, and sometimes all three symbionts are required to form a lichen. The fungus forms most of the structure, and the alga lives inside this structure, where it photosynthesizes and provides sugars to the fungus in return for a protected space to live. However, that is just the beginning when it comes to the uniqueness of a lichen. In, on, and throughout the scaffold of the main fungus and alga lives an unfathomably complex and diverse community of bacteria, non-lichen fungi, microscopic worms, and water bears. In many ways, lichens are miniature universes, better thought of as tiny ecosystems rather than strict symbioses between a single fungus and a single alga. No matter where your travels take you on land, you are almost guaranteed to find lichens. Lichens live on every continent, from the most extreme polar deserts to humid tropical rainforests. They serve dynamic and important roles in ecosystems, forming and stabilizing soil, fixing nitrogen and fertilizing forests, and providing food and nesting materials for animals from tiny insects to entire herds of caribou. In total, lichens cover around 8 percent of the land on the earth. However, lichens are not physiologically limited to habitats on our planet. There is no proof that extraterrestrial lichens exist, but experiments have shown they can survive the vacuum and radiation of space and grow in simulated Mars-like conditions. Although each individual lichen may be small in size compared

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with many plants and animals, their cumulative importance to our planet adds up to a vastness much more than the sum of their parts. Lichens are very sensitive to air pollution, a fact that was first noticed by lichenologists (people who are devoted to studying lichens) more than two hundred years ago. They thrive in pristine nature reserves and landscapes, but there are also hardy species that make their way into cities. Urban areas worldwide saw a steep decline in lichens beginning with the industrial revolution. In the United States, strict regulations on air quality that were implemented in the 1960s and 1970s have slowly reversed this trend, and lichens are gradually returning to cities. Throughout urban areas of northeastern North America, lichens have even made a big enough comeback that nature enthusiasts now routinely see them throughout cities and wonder what they are. Whether you live in the Bronx, Brooklyn, or Manhattan, Boston, Toronto, or Washington, D.C., if you look out your window and are lucky enough to see a tree or a rock, the chances are that you can see lichens. This book was written in response to the many requests we received for a resource to identify lichens in urban areas. Our initial inspiration was to focus on the lichens of New York City, but the flora we documented as a result, the “city community” of lichens, can be found in urban areas throughout northeastern North America. This includes the entire northeastern megalopolis from Boston to Washington, and cities in Canada like Ottawa and Toronto. For this book we took photographs of individual lichens found growing in the city in order to illustrate the “city morphology,” which is often markedly different from individuals growing in areas with better air quality. Our aim was to produce a book that would be accessible to everyone and anyone who might be interested in the organisms that we, the authors, already know and love. It doesn’t matter if you teach biology, are a student at the Fashion Institute of Technology, work for the Parks Department or as an administrative assistant at the City University of New York, serve drinks as a barista or bartender, or are any one of the countless other engaged citizens who form the dynamic fabric of cities. With a little practice, you will be able to use this guide to identify the lichens that grow around you. Having this goal in mind, we sought to cover the entirety of New York City for our field surveys, on foot, by subway, by bus, and occasionally by taxi. You can follow our lichen quests on your own and, like us, take in much of the diversity that spans the five boroughs and beyond. In the end we found more than one hundred species, and have included photos and descriptions here of more than sixty of those. Furthermore, as the air

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quality in New York City changes, and hopefully continues to improve, and climate change contributes to shifting species distributions, the lichen biota found in the city will continue to change. These changes could even happen rapidly, leading to a need for a new version of this book in only a decade or two. But that is the beauty of lichens. There is little doubt that, armed with this book as your guide, you could discover a new species that we didn’t find. Happy hunting!

The Lichen Lifestyle Basic Biology and Identification Overall Appearance The whole of the lichen taken together is called the thallus (plural, thalli). Lichen thalli can be characterized into three main types, or growth forms: crustose, foliose, and fruticose. The growth form typically gives the lichen its overall appearance, and even though lichens with similar growth forms are not always closely related, they are often grouped together for ease of identification. Crustose lichens have no observable lower surface and are instead completely attached to whatever they grow on. Due to their intimate contact with the substrate, crustose lichens usually cannot be removed intact without also removing some of the bark or rock on which they grow. Foliose lichens have thalli with lobes, are leaf-like, and always have clearly differentiated upper and lower surfaces, each of which is a different color. In foliose lichens the algae are kept in a single layer close to the upper surface, where they get enough light to photosynthesize. Squamules, aggregates of tiny, shingle-like lobes, are one type of specialized foliose growth form that is frequently encountered in cities. Fruticose lichens have thalli composed of branch-like, club-like, or cup-like structures and grow in three dimensions, resulting in a shrubby-looking appearance. Although the branch-like structures of fruticose lichens are typically round in section, they can be flattened and shaped like a blade. No matter what form they take, fruticose lichens can be separated from foliose lichens because they do not have clearly differentiated upper and lower surfaces. Instead, the branches are uniformly colored, whether the surface is viewed from above or below. Some fruticose lichens look like miniature shrubs, while others look like tinsel hung on Christmas trees. In the genus Cladonia the fruticose portions of the thallus, called podetia, are erect club-shaped or branching structures.

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crustose

foliose

fruticose Lichens are broadly categorized into three major growth forms: crustose, foliose, and fruticose.

The Lichen Within Distinct layers can be observed when a lichen thallus is cut longitudinally, as seen in a line drawing showing a foliose lichen in cross-section. The upper surface is what you see when viewing a lichen from above—this is the visible part of the upper cortex. The upper cortex is the topmost layer of the lichen and is composed of densely packed fungal hyphae, or filaments of cells that are the basic building blocks of all fungi, covered in a protective layer of sugars and crystallized chemicals secreted by the

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Upper Surface

Upper Cortex Algal Layer Medulla

Lower Cortex

Rhizines Lower Surface

A lichen is made up of multiple layers. The upper layer is a dense network of hyphae and sugars called the upper cortex. Below that is the algal layer, where the algae or cyanobacteria are held. Much of the lichen body is made of the diffuse inner mass of hyphae called the medulla. The bottom layer, the lower cortex, is another dense layer of hyphae and sugars. When looking at lichens in nature, the top of the thallus is called the upper surface, and if the lichen has a lower cortex, you can see the lower surface. fungus to prevent damage from ultraviolet radiation. In some lichens a cortex is lacking, and we call these ecorticate. The upper surface attracts water, and the ability to absorb water facilitates hydration as well as the transfer of minerals into the lichen. Just below the upper surface is the aptly named algal layer, where the cells of the photosynthetic partner, green algae or cyanobacteria, are found. Fungal hyphae grow mixed among the algal or cyanobacterial cells, holding them in place, moving them as they replicate, and harvesting the sugars they produce. Beneath the algal layer is the medulla. The medulla is usually the thickest layer of the thallus and is mainly composed of loosely arranged fungal hyphae. The hyphae in the algal layer and medulla are coated with special proteins, called hydrophobins, that are unique to fungi. Hydrophobins repel water, keeping it out of the gas-filled spaces inside the lichen, and helping to hold water inside the cells, where the liquid is needed for cells to function. Below the medulla is the lower cortex, which is another protective covering that encloses the thallus. The lower surface is the portion of the lower cortex that you can see when you look at the bottom of a lichen. Some

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lichens have hairlike outgrowths called rhizines that extend from the lower surface and anchor the lichen to the substrate that it is growing on.

How They Do It: Lichen Reproduction Fungi have some of the strangest and most complex sex lives in the natural world. Lichens are no exception, as they are composed mostly of fungi that have evolved a unique lifestyle that allows for even more reproductive diversity. Lichens can reproduce in multiple ways, often at the same time. Prepare to be amazed! There are two primary ways, or modes, that lichens can reproduce, and specialized structures are made for each mode. The simplest of these reproductive modes involves strictly asexual reproduction through vegetative fragmentation of the lichen thallus. In other words, pieces of the lichen break off, wedge into a crack on a tree or a rock, and begin to grow a new lichen. This form of reproduction is much like propagating succulents in your home by breaking off leaves and growing a new plant. Vegetative fragmentation occurs in nearly all lichen groups, and a third to half of the species in a given area will often be reproducing in this way. Asexual reproduction through vegetative fragmentation likely leads to rapid colonization of newly exposed surfaces in urban areas where environmental quality has improved. A more detailed explanation of the types of vegetative fragmentation that have evolved in lichens appears below, in the section on vegetative fragments. Although vegetative fragmentation is important to lichens, it normally leads to a profusion of genetically identical clones rather than genetically diverse groups of individuals. The primary way lichens maintain the genetic diversity needed to have healthy populations is through sexual reproduction. Sexual reproduction in fungi is governed by specific genes that control compatibility between thalli, called mating type loci. Some fungi keep their mating types in different individuals, so, just like in humans, two compatible individuals of opposite mating type must meet in order to reproduce. Other lichens carry everything they need in a single individual, and these fungi are able to self-fertilize and reproduce on their own without the help of a partner. At this point you probably get a sense that sexual reproduction in fungi is complex. For practical reasons, we will describe the simplest way that two mating types can meet, but it is helpful to keep in mind that, as is the case for humans, there are many ways to meet and begin a lifelong partnership. In the simplified process, one individual produces tiny flask-like structures called pycnidia that are lined with specialized hyphae

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Photobionts Germination

Photobionts Re-synthesis

Conidiospores

Re-synthesis Conidium Germination

Pycnidium Ascospores

Asci

Apothecium

Lichenized Diaspores (Soredia)

The lichen life cycle is complex, including sexual reproduction, asexual reproduction, and clonal propagation.

that continuously bud to release conidia, a type of clonal spore. These conidia ooze out the top of the pycnidia and are dispersed into the environment, where they eventually meet another individual. If they land on an individual of a compatible mating type (think boy meets girl here), then the conidium will fuse with a specialized structure called a trichogyne that looks roughly like a tiny pipe cleaner, and fertilization will occur. Once fertilization occurs, a fruiting body will develop, and sexual spores are produced there. After the sexual spores mature, they are released from the fruiting body and dispersed into the environment, where they germinate. At the time of germination, the fungus has to find a compatible algal partner, either in the environment or stolen from another lichen.

Types of Sexual Reproductive Structures The vast majority of lichens in cities are Ascomycetes, or sac fungi, one of the two main groups of fungi, the other being Basidiomycetes, which includes most mushrooms. Hence, here we discuss only the Ascomycete sexual reproductive structures. Although the sexual cycle in Basidiomycetes is conceptually similar to that of Ascomycetes, the structures

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have different names and morphologies. When the Ascomycete lichen fungus reproduces sexually, it forms fruiting bodies, and sexual spores, called ascospores, are produced in them. The fruiting bodies fall into two main categories. The majority of lichens in cities make apothecia (singular, apothecium), which are rounded, usually flat circular structures that resemble small discs or cups. From a distance, apothecia look like dots, which is the inspiration for many lichen common names. In a small number of species, the apothecia become elongated, sometimes even branched. An example of this is the script lichen, Graphis scripta. The second type of fruiting body is the perithecium (plural, peri­ thecia), which are typically dark-colored, flask-like structures that open through a tiny pore at the top. Compared with apotheciate lichens, there are relatively few species that produce perithecia in urban environments like New York City. Although differentiating between apothecia and peri­ thecia can sometimes be difficult, generally the upper surface of the apothecium is distinctly flattened and disc-like, while the upper surface of the perithecium is dome-like, with a tiny visible hole or dimple at the apex. Lichen sexual fruiting bodies are usually colored differently from the rest of the lichen thallus, making most of them stand out to the naked eye. Even though pycnidia are essential to sexual reproduction in lichens, they are often tiny, much smaller than the apothecia or perithecia, and difficult to observe. In many cases they are the same color as the thallus, or they are buried and visible only as minute spots on the surface.

Types of Vegetative Propagules Lichens have evolved many structures to disperse packets of fungi and algae together. These are known as symbiotic propagules or vegetative propagules. The two most common types of symbiotic propagules are soredia and isidia. Soredia are powdery particles composed of loose balls of intertwined fungal hyphae that surround one or a few algal cells. Soredia are often produced in delimited areas of the thallus where the upper cortex has broken open and the soredia are concentrated, which are called soralia. Isidia are finger-like projections from the upper surface that include fungal and algal tissue. The main difference between these two structures is that isidia remain enclosed in the protective covering of the upper cortex, while soredia do not. Pustules are one other type of symbiotic propagule commonly observed on lichens. Pustules are hollow, balloon-like outgrowths of the upper surface that eventually burst or break open. Pustules can then produce soredia or simply continue to break apart and peel away nearby areas of the thallus.

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Lichen Chemistry and Colors Lichens are a celebration of diversity and come in a full rainbow of colors, from red, orange, and yellow to green, blue, and every shade of brown and gray in between. This beautiful array of colors is a result of the incredible ability of lichen fungi to make thousands of chemical compounds that are unique and occur nowhere else in the natural world. These compounds are secreted by the fungus and crystallize around the hyphae. Often, compounds are produced and crystallized in highly localized portions of the thallus. For instance, the yellow pigments that give Candelaria concolor its distinctive color are restricted to the upper cortex. In contrast, the medulla of Phaeophyscia rubropulchra is pigmented orange-red because the compound that causes the color, skyrin, is restricted to that portion of the thallus. The color of most lichens is easily interpreted, such as orange and yellow. However, there are some subtle colors that can be difficult to discern. The two most commonly confused colors are “gray-green” or “grayblue,” which is the color of lichens that produce the chemical atranorin, and “yellow-green,” which is the color of lichens that produce usnic acid. These two colors are compared side by side below.

Usnic Acid Yellow-Green

Atranorin Gray-Green

Two of the most common lichen colors are yellow-green and gray-green / gray-blue. They can be difficult to tell apart when they are not side by side.

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The compounds that give lichens their distinctive coloration have functions beyond beautification. Many of the compounds have bioactive properties and likely aid in keeping unwanted bacteria or other microbes at bay. Some of the substances are also toxic in high dosages, and likely taste very unpleasant. These make the lichen unpalatable to lurking insects and snails that are always looking for a meal. Lichen compounds also have relevance to our society, as they can be used as natural dyes and for pharmaceutical purposes. It is important to note, though, that no species in the New York area is abundant enough to be harvested for any purpose.

Urban Lichens The increased interest in and awareness of urban biodiversity has closely matched the increased size of urban areas and human populations in cities. Urban landscapes currently cover roughly 3 percent of global land area. By 2030 that number is projected to triple, covering an additional 1.5 million square kilometers. Urbanization is a geologically recent addition to the natural landscape and closely follows the rise in industrialization and human population size. The proportion of the human population living in urban areas is more striking than the raw numbers of land area occupied, as 56 percent of people live in cities globally, and 70 percent are projected to live there by 2050. The increased interest in urban biodiversity has corresponded directly with an uptick in the study of lichens in urban environments. In the United States, such studies would not have been possible even a few decades ago, because air pollution had almost eliminated lichens from many cities. The loss of lichens from cities in Europe, North America, and some parts of Asia began during the industrial revolution. The Luxembourg Gardens in central Paris exemplifies this process, for it was by studying this system that William Nylander, a Finnish lichenologist living in Paris at the time, realized that air pollution has a negative impact on the growth of lichens. Nylander first reported thirty-two species from the park in the Bulletin de la Société Botanique de France in 1866. He published a second report on the garden in 1896, three years before his death, documenting the complete disappearance of lichens, and he attributed it to poor air quality resulting from the burning of fossil fuels in urban Paris. The absence of lichens from trees in the park was confirmed two years later by l’Abbé Auguste-Marie Hue, although he did occasionally find lichens on the calcareous balustrades. By 1943, when the next study on the Luxembourg

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23 species

Cincinnati, USA

66 species Alameda, Portugal

77 species 74 species 60 species Sheffield, UK

London, UK

Ruhr Valley, Germany

35 species Turin, Italy

83 species

25 species

Grenoble, France

138 species

Kolkata, India

Toronto, Canada

65 species

106 species

Kyiv, Ukraine

New York, USA

350 species Rome, Italy

127 species Geneva, Switzerland

296 species Singapore

28 species

Pretoria, South Africa

Lichens are recolonizing cities worldwide. In recent decades urban lichen studies have tracked their return.

Gardens was published, very little improvement in lichen diversity was evident. At that time Maurice Bouly de Lesdain still found no lichens on the trees, except for indistinct patches on one tree root that could not be readily identified. By 1986 Mark Seaward noted some small improvements, as he found one species on tree bases, and another, unidentified asexual species on the boles of trees. Seaward returned to the park in 1990 with a colleague, Marie-Agnès Letrouit-Galinou, and documented a remarkable return of eleven species that had recolonized the trees. The return of lichens had begun in Paris, and the story of the Luxembourg Gardens mirrors that of New York City.

New York City Lichens Through Time The first study of lichen diversity in New York City was published two hundred years ago by John Torrey, one of the most famous and productive botanists of the time. In 1819, Torrey reported sixty-one species growing within thirty miles of the town hall, which was located in lower Manhattan. Five years later, in 1824, Abraham Halsey, a Manhattan banker who was friends with John Torrey, published a list of 191 species he found growing within fifty miles of town hall. A near century-long period followed when

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there were no studies on New York City lichens. This gap in interest lasted until 1914, when New York Botanical Garden graduate student Charles Wood reported fifty-one species growing in the five boroughs of what was by then a united New York City. New York City lichens again fell into the shadows for almost half a century, until 1968, when Irwin Brodo published an exhaustive treatment of lichens from Long Island, including Brooklyn (Kings County) and Queens. Like many influential botanists of the twentieth century, Brodo was born in the Bronx and attended New York City’s public universities. To complete his work on Long Island, Brodo traveled throughout the region, visiting the then sleepy hamlets of the Hamptons and the distant points of Montauk and Orient. His work, undertaken after the industrial revolution and before President Richard Nixon signed the Clean Air Act, established the only such detailed baseline for a major American metropolitan area. This not only allowed for studies of how American urban lichen communities have changed through time, but also facilitated comparisons with our urban counterparts in London, Paris, and Tokyo. At the time Brodo finished his study, he found only eight lichen species inside the city limits of New York. His studies focused on parks in Queens and Brooklyn, but it was clear that lichens had essentially been eradicated from Manhattan, as well as large areas of the boroughs nearby. Those that did survive were mostly disfigured and scraggly, relegated to the edges of the city, or to parklands such as the Brooklyn Botanic Garden and Prospect Park. Since that time, the air quality of New York City has steadily improved, and the lichens have responded in kind. There are now approximately one hundred species spread throughout the five boroughs. We should all appreciate what a wonder it is to witness the return of these beautiful fungi for the first time in more than a century.

Why Are Lichens Affected by Air Pollution? A poem that Erasmus Darwin wrote in 1791 is often cited as the first rec­­ ord of the sensitivity of lichens to air pollution: No grassy mantle hides the sable hills No flowery chaplet crowns the trickling rills Nor tufted moss nor leathery lichen creeps In russet tapestry o’er the crumbling steeps

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It is sometimes thought that Darwin wrote this while observing the copper mines at Parys Mountain, Wales, but he was in fact referring to a poison tree in Java. The romantic among us may still choose to take these bleak observations as the first record of a scientist reporting the impacts of pollution on lichens. However, its claim to be the first is contentious, as it is vague and a poem. The indisputable first direct observation was recorded by William Borrer in 1807, when he wrote, in regard to urban conditions in England, “the air is so impure that scarcely any other lichen can exist.” Since the initial recognition of the link between poor air quality and lichen death, research on how and why this phenomenon occurs has accelerated. Indeed, monitoring air quality is the most important way that humans have used lichens in the twentieth and twenty-first centuries, as it is much less expensive and just as effective as deploying air-quality monitoring devices. By documenting which species occur in an area, it is possible to determine both the type and severity of air pollution. Lichens are continually exposed to the air and their environment. In certain conditions, pollutants that land on lichens are absorbed by the thallus. Chemicals can cause damage to lichens once they are absorbed. Sulfur dioxide is the most toxic compound for lichens, as it is usually converted to highly acidic bisulfate in the environment, which then interrupts normal cell functioning upon absorption by the thallus. Free radicals are also produced in abundance when sulfur dioxide is taken up by lichens, and these act like small internal ballistics and cause severe damage to cells. Some nitrogenous compounds cause acidification of the substrates that lichens grow on, while others cause substrates to become more alkaline. Although the negative consequences of these effects for lichen individuals are not as extreme as from sulfur dioxide, it literally changes the ground beneath the lichen’s feet. A given lichen species can be sensitive to either one or both of these types of pollutants. Most lichens that find their home in New York City are tolerant of both acidic pollution and fertilizing, or nitrogen-based, pollution. However, the levels of sulfur-based pollution have been reduced in recent years to the point that a few acid-sensitive species have recolonized. As can be seen in a table of species reported from New York City that have air quality response ratings (Table 1), using only a small subset of foliose and fruticose lichens as indicator species makes it simple to conduct your own neighborhood air quality assessment. Do any of these species occur around where you live? How frequently do you see them? Are any of the sensitive species present?

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Table 1 Air quality sensitivity ratings for some lichens that occur in urban areas of the Northeast

Indicator Species

Response to Acidic Pollution

Response to Fertilizing Nitrogen

Overall Sensitivity to Air Pollution

Candelaria concolor

Tolerant

Tolerant

Tolerant

Cladonia cristatella Flavoparmelia caperata

Tolerant Sensitive

Tolerant

Hyperphyscia adglutinata

Sensitive Tolerant

Parmelia sulcata

Tolerant

Tolerant

Parmotrema hypotropum

Sensitive

Phaeophyscia pusilloides

Tolerant

Tolerant

Tolerant

Phaeophyscia rubropulchra

Tolerant

Tolerant

Tolerant

Physcia adscendens

Tolerant

Tolerant

Tolerant

Physcia millegrana

Tolerant

Tolerant

Tolerant

Physcia stellaris

Tolerant

Tolerant

Tolerant

Sensitive

Physciella chloantha Punctelia rudecta

Tolerant

Tolerant Sensitive

Usnea sp.

Sensitive

Sensitive Sensitive

Source: Will-Wolf et al. 2015

Lichen Chic

Fashion, Finance, and Fortune Shades of yellow and brown are easy colors to come by in plants for dyeing fibers. Purple, on the other hand, is exceedingly rare. Given how fabulous lichens are, it should come as no surprise that they are one of the few sources of purple dye in the natural world. Cultures worldwide and over millennia have harnessed this unique property of many lichen species, along with the myriad other incredibly diverse unique chemical compounds they make, as a source of dyes for textiles. The oldest completely purple garment was discovered from a Chinese burial site more than four thousand years old. This may be the

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Lichens are a source of natural dyes. All of the wool in this photograph was dyed with lichens. oldest lichen-dyed textile uncovered to date, but the exact source of the purple remains a mystery. The other common natural source of purple is a small gland in mollusks. Huge quantities of shellfish are required to produce even small amounts of dye, which quickly led to overharvesting in the ancient world, and the subsequent discovery of lichens as an additional source. The first written recipe for lichen dyes was recorded in the year 200, from a Greek text called Papyrus Homiensis. The recipe uses a species of Roccella, a genus of lichens common throughout the Mediterranean coast. However, as is the case with many species of economic importance, the use of Roccella was shaped by cycles of overharvesting. In the fourteenth and fifteenth centuries, when Italy was ruled by feudal city-states, the demand for purple fabrics for daily use and export were at an all-time high. People in the higher social echelons distinguished themselves from the common crowd by wearing purple, a color few could afford at the time. As a result, both the mollusks and the lichens were overharvested in vast quantities.

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The second period in history when demand for lichen dyeing surged, and species were collected to the point of eradication, was centuries later, during the industrial revolution. At that time lichen dyes became one of the major drivers of the Scottish economy. The distinctive colors in Harris tweed resulted from boiling “crottle,” Parmelia omphalodes and Parmelia saxatilis, and from fermenting “cudbear,” Ochrolechia tartarea, which grows on rocks in Scotland and other regions, in ammonia. Today you can go to the grocery store and buy a bottle of ammonia when you need it, but this was not possible back then. Instead, dyeing factories would purchase urine from the people of Edinburgh and ferment the lichens in large open vats of the liquid. Producing the dye on such a large scale quickly led to the overharvesting of cudbear. Factory owners tried to switch to rock tripe lichens (members of the family Umbilicariaceae) imported from Nordic countries. However, the fermentation recipe and timing using rock tripe was too different from the cudbear recipe, and the whole operation, for better or worse, fell apart before the methods could be adjusted. In modern times, the advent of industrial chemical engineering has eliminated the economic niche that the lichen dyeing industry once occupied. Fabric today is dyed primarily with a variety of synthetic pigments, removing the need to harvest vast quantities of lichens to achieve luxurious purples and reds. Only a small but passionate community of textile artists and craftspeople continue to dye with lichens. Most people interact with lichens in other ways, usually without knowing it. Usnic acid harvested from lichens is often used as an ingredient in all-natural toothpaste and deodorant, although the compound can be toxic in higher doses, so one should be wary of lichen tinctures. Window displays frequently incorporate reindeer lichens (Cladonia species, most often C. subtenuis and C. rangiferina); they are almost always spray-painted bright and gaudy colors, however. The wolf lichen (Letharia vulpina), native to the western United States, has more recently become a favorite display décor. Patterns and pictures of lichens can also be found incorporated into art and fashion in more places than you expect. With your newfound lichen spotting abilities, keep an eye out for lichens as you go through your day-to-day life, and you will be surprised how frequently you encounter them. It is important to be careful when purchasing lichens, as their collection for economic purposes is not regulated, and the impacts of harvesting on lichens are poorly understood. There are few, if any, cases where industrial-scale harvesting of lichens could be done sustainably with current knowledge. Similarly, if you are harvesting lichens for culinary,

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Lichens are often harvested to use as décor. This Cladonia would be gray or white in nature, but was dyed bright yellow and placed in a potted plant at a pizzeria on the upper west side of Manhattan. medical, or dyeing purposes, there are two things to be aware of. First, be very careful how much material you take. Never collect lichens if there are very few individuals of the same species nearby, and never collect all individuals from any given area. Rare species can easily be accidentally harvested, as their differences from more common species are often subtle. Second, since lichens sequester pollutants from the environment, it is important to remember that your lichen could contain heavy metals and other toxins. Be sure your identification skills are sharp before conducting any lichen harvesting. Land management agencies, like national forests and city parks, all have rules and regulations for harvesting natural products, so make sure you understand these before beginning any collecting activities.

Lichens and Animals Nature works through connections: like a large, three-dimensional web, where each species is a connection point and interactions are the strands between the connections. Even seemingly small, insignificant organisms are tied to innumerable other species. Lichens connect and interact with a vast array of animals, acting as a hub of activity, and a fulcrum between microscopic and macroscopic organisms. They provide essential food sources, nesting material, camouflage, and even entire homes for some animals.

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The most famous lichen gourmands are caribou, or reindeer. For a tundra caribou, lichens are the foundation of the food pyramid. An adult tundra caribou can eat more than three kilograms of lichens in a single day as it migrates across the arctic region. Woodland caribou are similarly dependent, especially in the winter. Not all lichens are tasty snacks, as some have high concentrations of unsavory acids, but caribou have excellent lichen identification skills and can smell the difference between palatable and unpalatable lichen species. The recent disappearance of woodland caribou from the Selkirk Mountains in western North America is likely tied to a drastic loss of lichens in that region due to logging activities. Both woodland and tundra caribou are threatened today, and their populations are in steep decline. One major reason for the widespread decline in caribou is the loss of lichens that results from the extraction of resources and rapidly melting permafrost. Many other large herbivores are reliant on lichens for at least part of the year, including moose, deer, and big-horned sheep. Smaller mammals often incorporate lichens as part of their balanced diet. Rabbits and voles, for instance, can be seen nibbling lichens here and there. For northern flying squirrels, lichens do double duty. Flying squirrels will line their nests with lichens in the fall, as they provide a warm, dry insulation with built-in antibacterial and antifungal compounds. As the winter draws on the squirrels will slowly eat away at their nest until spring arrives and food sources are abundant again. Some birds harness these same properties of lichens in their nest building, including the snowy plover and many species of hummingbirds. In the case of hummingbirds, the lichens act as an excellent camouflage for their precious eggs. If you start looking closely at lichens on a frequent basis, sooner rather than later you will notice a lichen move. Well, the lichen is not moving, but an insect or a spider that is exquisitely camouflaged with a lichen will twitch and make itself seen. There are frequently grasshoppers nestled in lichens, and tropical katydids, a cousin of grasshoppers, are so perfectly evolved to resemble lichens that they don’t even have to stick close to their mimicked species. A real treat is seeing lacewing larvae with a coat of dust lichens (Lepraria species) glued all over their backs. When the larvae are ready to grow into an adult they finish their dust lichen coat and enclose themselves in a complete ball, then cut themselves out to fly off once they are fully developed. Mites and ants, though not camouflaged to look like lichens, can often be found living on or under thalli, using them to build their colonies. Even smaller animals live inside lichens, making their

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homes between the hyphae. Water bears (tardigrades) and nematodes graze through the lichens, munching on fungi, algae, and bacteria while being protected from the harsh surrounding environment.

Hunting Lichens in Cities What Lichens Grow On Lichens most frequently grow on bark, rocks, sidewalks, wooden fences, and soil. Some lichens, particularly crustose species, can also be found living in the cracks and divots of bricks, mortar, and stonework of older city buildings. However, if you pay close attention, you can even find them on what may seem to be trash. Discarded materials that lichens are most frequently found on include metal, such as cans or rusted-out cars, and fibers, like clothes and couches.

Bow Bridge

Brooklyn Bridge

Bethesda Fountain

Lichens are all around you. Take a look at the trees, stonework, and sidewalks as you go about your day and you may be surprised how many there are.

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Lichen Look-Alikes If you examine some vaguely white, green, blue, red, or yellow film on a tree or sidewalk and cannot seem to match it with any species in this book, it may not be a lichen. There are a number of lichen look-alikes that can be confusing. Paint, especially old trail markers on trees, is the most usual suspect. There are no bright blue lichens, so it’s easy to exclude blue markings, but white can be a bit trickier. If the surface of the white scuzz in question is shiny and hard, then it is paint and not a lichen. White scuzz can also be old gum wads and bird poop, so you may not want to look too closely. Fungi that are not lichens may also be mistaken for lichens. These non-lichen fungi are often small and observed growing on branches or dead wood debris and wood fences. They aren’t mushrooms, as you usually imagine fungi looking, but instead are often small black specks that can be rounded or elongated. Other fungi are pink or white. In some cases, non-lichen fungi can even grow on top of actual lichens. A great example seen occasionally in the city is Athelia arachnoidea, a lichen parasite that appears as orange-tinged webbing over a thallus. If you aren’t sure whether or not it’s a lichen simply give it a bit of a scratch and look for the bright green algae inside. Free-living algae also grow on trees and rocks throughout the city, especially in areas that are cool, humid, and damp. Patches of algae are a darker green than lichens, and do not closely resemble any of the species that are illustrated in this book.

Collecting Lichens Lichens can be strange, beautiful, captivating, and inspiring. These qualities sometimes tempt observers to take lichens from their environment for personal collections, or other reasons. However, lichens are just now making their way back into cities like New York and are generally sensitive to disturbance. Please do not collect lichens unless you are conducting a scientific study, in which case you should seek guidance from an expert before you begin. It is essential that we all help, rather than hinder, the return of lichens. Instead of physically collecting lichens you observe, we recommend collecting photographs, drawings, or written descriptions of your observations. These lichen-friendly approaches to naturalism are ecologically thoughtful ways to enjoy the urban lichens without interfering with their slow but steady recovery.

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New York City Lichen Hot Spots There are hot spots for every activity in New York City, whether it be seafood dinners on City Island, ice skating in Central Park, Mets games in Queens or Yankees games in the Bronx, sunsets on the Staten Island Ferry with beers on a date, the latest new ice cream shop or the old mainstay jazz club. Sometimes it is just coquito from a cart on the corner of 103rd Street and 3rd Avenue on a sweltering day. Lichens can be found sprinkled on the sidewalk trees and caked in the mortar on apartment buildings in almost every neighborhood, but there are parts of the city with exceptionally diverse and abundant lichens. These hot spots can be found in every borough, and the only velvet rope is a MetroCard swipe and the occasional entrance fee to a cultural institution. Remember, though, we have provided these suggestions based on our experiences and search effort, but the hottest spot is usually the one that hasn’t yet been discovered. Hot spots in the Bronx: Woodlawn Cemetery on large old trees and old stonework; the New York Botanical Garden in the native forest on bark, soil, and shaded rocks Hot spots in Brooklyn: Brooklyn Botanic Garden in the rock garden and bluebell wood; Prospect Park in The Midwood Hot spots in Queens: Alley Pond Park north of Hogato Playground; Astoria Park on large trees around the Great Lawn and the North Lawn Hot spots in Manhattan: Inwood Hill Park; Central Park North Woods; Fort Tryon Park Hot spot in Staten Island: Freshkills Park in woodlands adjacent to Schmull Park

Fifty Lichens in One Day A Whirlwind Tour of New York City

Are you strapped for time but dying to see all of the lichen wonders New York City has to offer? Maybe just in town for a twenty-four-hour layover between flights in and out of JFK as part of a globe-trotting adventure. Well, you can see all the sights that our city has to offer and take in fifty lichen species all at the same time! Here’s how:

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⦿ 8 a.m., Astoria Park, Queens Most outstanding species: Caloplaca feracissima, Physcia millegrana, and Candelaria concolor Rare finds: Myelochroa aurulenta, Punctelia caseana, and Trapelia placodioides ⦿ 10 a.m., The New York Botanical Garden, Bronx Most outstanding species: Punctelia rudecta, Physcia thomsoniana, and Lepraria neglecta Rare finds: Cladonia rei, Endocarpon pallidulum, and Parmotrema hypotropum ⦿ 12 a.m., Lunch on Arthur Avenue ⦿ 1 p.m., Central Park, Manhattan Most outstanding species: Flavoparmelia caperata, Xanthoparmelia plittii, and Sarcogyne clavus Rare finds: Cladonia grayi, Pyxine subcinerea, and Acarospora fuscata, Flavopunctelia soredica ⦿ 3 p.m., Brooklyn Botanic Garden and Prospect Park, Brooklyn Most outstanding species: Cladonia species, Physcia stellaris, and Punctelia caseana Rare finds: Xanthomendoza fallax, Lecanora hybocarpa, and Hyperphyscia adglutinata

right Many objects and organisms can be confused with lichens. Pictured here are some of the most common look-alikes.

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Jelly Fungus

Gum

Shell Fungi

Paint

Paint

Slime Mold

Free-Living Algae

Lichen Parasite Fungus

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the sp

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spEcIeS This section includes detailed descriptions and discussions of sixty-one of the most common lichens encountered in urban areas of the Northeast. Each species treatment includes one or more photographs, a technical description, where it can be found, abundance ratings, and notes on how to distinguish it from similar-looking species. Some species have official air quality ratings, and those are included at the end of relevant treatments. The ratings are from Will-Wolf et al. (2015) and broken down into three different subsets: overall, acidic pollution, and fertilizing nitrogen. Some species have ratings for only one category, while others have ratings for all three categories. The species are organized first by growth form: crustose, foliose, and fruticose. Within each growth form the species are organized by thallus color: blue-gray, gray and white, brown and green, yellow and yellow-green, and invisible; the colors are based on observations made when the lichens are dry. Then, in each color, the species appear alphabetically by scientific name. Items included in the photographs for scale are coins and a MetroCard, which is used to access the New York City public transportation system and is about the size of a credit card; shown in the accompanying sketch here are the sizes of these items in inches and centimeters.

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CRuStoSE SpecieS

old gray dust

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Blue-Gray

Old Gray Dust

Lepraria caesiella R.C. Harris Description  Thallus crustose, distinct, well-developed, leprose, granulose, powdery, thin; upper surface blue-gray to gray, fuzzy, dull; prothallus indistinct or white; vegetative propagules present, granules, forming the entire leprose thallus, blue-gray to gray, coarsely granular, the granules