Marin Flora: Manual of the Flowering Plants and Ferns of Marin County, California [Reprint 2019 ed.] 9780520313576

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MARIN

FLORA

Madroño (Arbutus Menziesii) in the tanbark oak-madroño forest near Mountain Theater, Mount Tamalpais.

MARIN FLORA Manual of the Flowering Plants and Ferns of Marin County, California By JOHN T H O M A S H O W E L L PHOTOGRAPHS BY CHARLES T. TOWNSEND

UNIVERSITY OF CALIFORNIA PRESS B E R K E L E Y AND LOS

1949

ANGELES

UNIVERSITY OF CALIFORNIA PRESS BERKELEY AND LOS ANGELES CALIFORNIA

CAMBRIDGE UNIVERSITY PRESS LONDON, ENGLAND

COPYRIGHT, 1 9 4 9 , BY T H E REGENTS O F T H E UNIVERSITY O F CALIFORNIA

P R I N T E D IN T H E UNITED STATES O F

AMERICA

BY T H E GEORGE BANTA PUBLISHING

COMPANY

Preface THE METROPOLITAN area about San Francisco Bay is noted for the ease with which one may get from crowded cities into open country. For many decades, Marin County has been considered one of the most scenic parts and its hills and forests have been a constant lure to those who wish to lose themselves in the beauty of a natural scene. In 1938 I turned to the Marin countryside for weekly recreational walks, and, to add a botanical motive to my outings, I began almost immediately to collect data on the rich and diverse flora which was everywhere about me. T h e elaboration of these simple data, so pleasantly acquired, has resulted in the present work. My aim has been to prepare a usable tool with which both amateur naturalist and student can become familiar with a remarkable flora lying within ready access of more than a million people, and no effort has been spared to give as accurate and full an account as possible. Although my botanical field studies in Marin County have been pursued more intensively for the past ten years from the California Academy of Sciences, they actually began over twenty years ago while I was still a student of W. L. Jepson. Over this period of years almost every part of the county has been explored, and some places, such as Mount Tamalpais, Point Reyes Peninsula, and Tiburon Peninsula, have been visited many times. Even after this prolonged and detailed survey, plants new to the area are being found, and because so many of the species in the region are characterized by an extremely localized occurrence or restricted range, they will probably continue to be found. It was originally hoped that the present work would be relatively simple and nontechnical, but such an aim has been only partly realized. In a flora as extensive and as diverse as that of Marin County, there is no way of preparing keys for the identification of the plants without recourse to scientific terminology. T h e meaning of these botanical terms can be found in the glossary preceding the index at the end of the book. T h e details in the keys given for the determination of family, genus, species, variety, or form apply only to the plants of Marin County, though much of the data should hold for central coastal California. T o save space, descriptions of the different groups, from families to forms, are not given beyond the points needed to identify them in our region. Students desiring a fuller treatment of a plant will find it described in detail in the floras of L. R. Abrams or W. L. Jepson, either under the name used for the plant in this work or under the synonym placed at the end of the ecologic and distributional note that is given for each Marin County plant recognized. Synonymy, beyond this kind supplied for reference purposes, is rarely given. Systematic work in botany, whether it is floristic or monographic, leans so heavily on what has been done by others that excessive pretensions to novelty and originality can generally be discounted. Of the utmost importance and help in assembling floristic data in the present work was a manuscript catalogue of Marin County plants given to me by the late John W. Stacey. A shorter general list was received from Dorothy Sutliffe and a catalogue of plants found [v]

vi

PREFACE

in the Sausalito Hills was received from Elsie Zeile Lovegrove. T h e Stacey catalogue approached the proportions of a complete flora, 1,006 species being listed from many localities. T h o u g h its importance and usefulness in the present work can be realized by the n u m b e r of times it is referred to for records of occurrence, it is to be regretted that botanical specimens substantiating these records are usually lacking. Besides the help from these three lists, many field records and specimens have been provided by Hans Leschke, whose name also appears frequently with the others at appropriate places in the text. Numerous other records have come from Alice Eastwood—in conversations with her, from her extensive writings, or from her abundant Marin collections preserved in the Herbarium of the California Academy of Sciences. In the present work, the western America floras of L. R. Abrams, W. L. Jepson, T . H. Kearney and R. H. Peebles, P. A. Munz, and M. E. Peck, as well as the floristic works of others, have been consulted constantly, and the works of L. H . Bailey and A. Rehder have been referred to frequently in connection with the identification of naturalized garden plants. Wherever possible, account and use have been made of pertinent revisional notes and monographic studies of many students. Most of the American botanists who are authorities on families or genera represented in the Marin flora have generously answered questions, identified specimens, and given other taxonomic or bibliographic help, and to all these I am very grateful. It is from all these sources that the presently acceptable name for each Marin County plant, as interpreted in my judgment, has been obtained. Besides the debt owed to many for botanical assistance, I also wish to express special gratitude to the following: R u p e r t C. Barneby, who has read the manuscript and contributed many helpful suggestions; Hans Leschke, who has not only read the manuscript b u t has also been a keen and constant collaborator in field work; Thomas H. Kearney, who has helped to clarify many problems, botanical and bibliographic; Lewis S. Rose, who has cooperated in field work and has assisted in many ways in the herbarium; Evelyn M. Deasy, who has prepared the manuscript. A special debt is owed to Charles T . Townsend for his fine photographic record of the Marin scene and to Malcolm G. Smith who has drawn the maps. Finally, I wish to acknowledge my obligations to the California Academy of Sciences, which for nearly a century has been the scientific institution nearest to Marin County, and to Alice Eastwood, its Curator of Botany, who for over fifty years has been the one most concerned with Marin County plants. J. T. H.

California Academy of Sciences November 22, 1948

Contents Introduction

1

Location and Physiographic Features

1

Geologic Structure and Rocks

2

Soils

4

Climate and Weather

4

Life Zones and Plant Associations

5

Effect of Fire

21

Numerical Analysis of the Flora

23

Geographic Distribution of Plants in Marin County

23

Marin County Flora and Flora of Coast Ranges . . . .

25

Endemic Plants

27

Naturalized Plants

27

Early Botanical Explorers

28

Later Botanical Explorers

30

L'envoi

33

Keys to the Groups and Families

35

Enumeration of the Flora

49

Principal References

295

Glossary of Technical Terms

297

Index of Names

307

Maps of Marin County and Mount Tamalpais [vii]

321

Introduction PHYSIOGRAPHIC

FEATURES

WHEN JOHN C. FREMONT proposed the name Chrysopylae, or Golden Gate, for the narrow channel between San Francisco Bay and the Pacific Ocean, he could hardly have known that within a few decades the works of man would have all but obliterated that which was natural on the southern shore of the channel. T o the north in Marin County, however, beyond the small towns and cities, long stretches of country are altered only as cattle have grazed and man has cut timber, built roads, or cleared ground; in spite of its proximity to a world port and metropolis, the landscape still displays a wildness and natural beauty that have been but little impaired. For the hills along the north shore have for the most part been kept as military reservations and the slopes of Mount Tamalpais are mostly included in federal, state, and municipal preserves. T h e marshes and hills along the bay have been little affected by dredging and filling; the coastal bluffs and ridges of Point Reyes Peninsula are much as they were when Sir Francis Drake landed in 1579; and the broad open hills at the northern end of the county must still appear as they did to the Russians, when, more than a hundred years ago, those colonists looked southward across Bodega Bay from the Sonoma hills of Russian America to the Marin hills of Alta California. Indeed, throughout the 529 square miles of the Marin County Peninsula, the scenes of beauty are an encouragement and an invitation to see and learn more of nature. Marin County has remained relatively wild and large cities have not been built along its shores chiefly because of its hilly, even mountainous, topography. Nearly everywhere hills and wave-cut bluffs rise from the water or tidal marshes, and only occasionally is there level or gently sloping ground where hills are more gradual or where narrow valleys and canyons enter the bay or ocean. Along the Golden Gate the rise from the water is so abrupt that the highest point in the Sausalito Hills, 960 feet, is attained in less than a mile; the slope east of Stinson Beach rises 2,000 feet above the ocean in little more than a mile; and the precipitous bluffs at Point Reyes have an elevation of 600 feet. Sand beaches are mostly small and narrow and are restricted to the heads of coves except in several notable places. At the head of both Bolinas Bay and Drakes Bay remarkable sandspits have developed which almost cut off from the ocean Bolinas Lagoon and Drakes Estero, and along the ocean north of Point Reyes and again north of Tomales Bay are long broad beaches and the most extensive dunes in the county. T h e Point Reyes beach and dunes have completely cut off from the ocean Abbotts Lagoon, a freshwater sandbar lake; and at Dillons Beach, Rodeo Lagoon, and other places, larger or smaller ponds of fresh or brackish water have been formed behind beaches and dunes. Elsewhere, particularly along San Francisco Bay and at the head of Tomales Bay, broad marsh lands penetrated by meandering sloughs and tidal channels are a distinctive feature. But nearly everywhere, beyond the marshes, back of the beaches, above the seacliffs, is the hill country of Marin County.

[1]

2

MARIN

FLORA

T h e hills are frequently aligned or grouped to form rounded or elongate ridges, separated from one another by passes, canyons, or valleys. Three of these ridges project into the bay as Tiburon, San Quentin, and San Rafael peninsulas, while two circular areas to the south are Angel Island, separated from the mainland by Raccoon Strait, and the Sausalito Hills, cut off from the adjacent hill country by a low pass between the bay and the ocean known as Elk Valley. North of Elk Valley rise the hills that culminate in Mount Tamalpais, 2,610 feet in elevation, the highest and most prominent point in Marin County. Since the slopes of the mountain rise abruptly from the bay and from the ocean, it has a beauty and impressiveness usually found only in peaks much higher, and deep, steep-walled canyons separated by sharp rocky ridges add to the general wildness and interest of the scene. This country of rugged relief, of which the summit of Mount Tamalpais is the highest part, extends to the north for some distance, and is bounded by Ross and Nicasio valleys and the lower part of Lagunitas Creek. In this area there are the well-defined elevations of Bolinas, Carson, and San Geronimo ridges, and the uplands are dissected by the deep canyons of Lagunitas and Corte Madera creeks and their tributaries. T h e ruggedness of this country in many parts is such that, if one is off roads and trails, travel may be arduous and a cross-country trip may still be difficult and adventurous. Beyond this rugged Tamalpais area and north to the Sonoma County line, the valley lands are more ample and the slopes of the hills are usually less abrupt. Nowhere does an elevation exceed 2,000 feet, though that height is approached at the top of Big Rock Ridge, elevation 1,905 feet, and Burdell Mountain, a little farther north, 1,560 feet in elevation. These ridges, like Mount Tamalpais, rise from near sea level, but they lack the bold contours of that mountain and are therefore not so impressive. G E O L O G I C STRUCTURE AND

ROCKS

On the west, the Tamalpais highland is bounded by a narrow valley which, together with Bolinas Lagoon on the south and Tomales Bay on the north, separates Point Reyes Peninsula from the rest of Marin County. T h e most prominent topographic feature of this part of the county is Inverness Ridge, the long straight ridge that parallels the narrow valley and the bays at either end. T h e ridge is not high, the highest points being Mount Wittenberg, 1,403 feet, and Mount Vision, 1,336 feet, but the narrow elongate highland is regular, with only Bear Valley breaking its continuity. On the east front it is quite steep, but on the west it slopes more gradually to the edge of precipitous ocean bluffs, to the marshy borders of Drakes Estero, and to the broad coastal downs above the Point Reyes dunes. T h e straight narrow valley which separates the Tamalpais area from Point Reyes Peninsula is noteworthy not only from the physiographer's point of view, but also from the geologist's, since it lies along the San Andreas Fault and represents one of the most pronounced and remarkable fault-trace features in this part of California. This fault, which extends northward from the Gulf of California through the mountains of southern California and the South Coast Ranges, crosses west of the Golden Gate between the mainland and the Farallon Islands and enters Marin County at Bolinas Lagoon. After extending along the fault-

GEOLOGIC S T R U C T U R E AND ROCKS

3

trace valley and Tomales Bay in Marin County, it passes across the Bodega roadstead, separates Bodega Head from the mainland in southern Sonoma County, again passes out into the ocean, and reappears on the mainland for the last time in northern Sonoma and southern Mendocino counties, before finally disappearing in the depths of the Pacific just north of Point Arena. It was along the northern part of the San Andreas Fault that the movement took place which, in 1906, caused the earthquake that resulted in the disastrous San Francisco fire. While the fault line in Marin County is most prominently marked by the rift valley and the steep escarpments of Inverness and Bolinas ridges, there are also other less conspicuous features associated with it, such as trenching, sag ponds, displaced hills and streams, and fault breccia. Although these physiographic features make the area unusually interesting, the chief significance of the fault line is that it separates regions with different geologic histories. East of the fault, the rocks are very old and belong to a series known as the Franciscan Group which is generally believed by geologists to belong to the Jurassic period of geologic history. These rocks are largely sedimentary and consist of shales, sandstones, and conglomerates, together with sometimes local and sometimes extensive occurrences of radiolarian chert. Intruded into these sediments are basic igneous rocks, which, like the outcrops of the chert, may be localized or more extensive. T h e most conspicuous occurrences of these igneous rocks are in those areas where one of them has been metamorphosed to form serpentine, a very distinctive rock type that is common on Tiburon Peninsula, Mount Tamalpais, Carson Ridge, and in other places in the Franciscan area. T h e noteworthy geologic feature of the southern and middle part of Marin County is that there is no trace of younger rock formations anywhere, the only recent sedimentary accumulations being the dunes and beaches along the shore and the limited soil deposits on level ground of valley and coastal flats. This fact indicates that Mount Tamalpais and the surrounding area belong to an ancient upland or mountain mass that has been above sea level as long as any area in western coastal California and much longer than most areas; otherwise sediments of younger formations would be found overlying the ancient Franciscan rocks. This old formation is widespread in the Coast Ranges, but almost everywhere it is found together with younger sedimentary rocks that were deposited on the Franciscan series at a time when that particular area was depressed or below sea level. This is the condition that prevails in Marin County north of the Tamalpais physiographic area, for there the Franciscan rocks are overlain by sediments of Pliocene age and along the ocean there are localized beach deposits of Pleistocene age. T o the west of the San Andreas Fault another very old rock is found, but unlike the sediments and intrusive igneous rocks of the Franciscan formation, this rock is granite. T h e occurrence of this coarsely crystalline igneous type is rather extensive along Inverness Ridge near Inverness and at the northern end of the peninsula, and there is a localized outcrop near Point Reyes. T h e granite is not so easy to recognize when it is much weathered, but the granitic ocean cliffs at McClure Beach are distinctive and much of the beauty of the bluffs at Shell Beach comes from the granite of which they are composed. This type of granite, which is commonly known as Montara granite because of its occurrence on Montara Mountain south of San Francisco, has never been found east of the

4

MARIN

FLORA

San Andreas Fault, but to the west it has been found not only in Marin and San Mateo counties, but also on Bodega Head in Sonoma County, Cordell Bank west of Point Reyes, Farallon Islands in San Francisco County, and far to the south on the Monterey Peninsula and in the Santa Lucia Mountains in Monterey County. Wherever it occurs, the granite is generally overlain by much younger sediments. On Point Reyes Peninsula these rocks are of several kinds. Most common and widespread are the pale bedded rocks of shaly character that have been referred to the Monterey series of the Miocene epoch, a formation covering most of the peninsula west of Inverness Ridge. On the west side of Bolinas Lagoon and extending a little to the north along the San Andreas Fault are Pliocene marine sands that overlie the Monterey series in that area, and near Point Reyes is again a localized Pleistocene beach deposit. Then on top of these relatively young formations are the very recent beach and dune deposits, already described. SOILS

In regions having a desert climate it is generally much easier to examine the geologic structure and study the rocks than in places like Marin County, where, owing to the moderate amount of rainfall, the rocks break down in a relatively short time to form a layer of soil. Most of the area is covered with clayey or sandy loam, depending on the character of the underlying rocks; but in many places the terrain is too steep for the soil to remain in place and landslides are frequent. T h u s there are many rocky blulfs along the shoreline, and on the more abrupt slopes of hills and canyons, rock outcrops are frequent and sometimes extensive. T h e rugged country of the Tamalpais physiographic area is especially rocky, and on the steep slopes of Mount Tamalpais itself the soil layer is usually very thin or even entirely lacking. Outcrops of chert and serpentine—slowly weathering rocks—are generally easily recognized since they are frequently quite devoid of a soil cover; nevertheless, some soil accumulates in level places and mingles with broken fragments of the substratum. Adjacent to dune areas along the coast the soil becomes increasingly sandy as the beach is approached, and a dune-derived soil of considerable depth may develop. Deep soils also collect as an alluvium in the restricted valley bottoms or along the base of hills, and this deep wash soil may merge locally with siltlike deposits on tidal flats, especially along the bay and the maritime esteros. C L I M A T E AND W E A T H E R

T h e Marin climate, like that of most of coastal California, is characterized by warm dry summers and cool rainy winters, the same general type of climate that is found in the Mediterranean regions of southern Europe and northern Africa. T h e Pacific Ocean and the fog, however, have a more moderating effect than the Mediterranean, and the annual range of average temperature is not so great as it is farther inland in California. T h e extremes of temperature recorded for specific stations in Marin County may vary by as much as 95° Fahrenheit, while the mean temperatures for January and July may differ by only a fourth to a third as much. Thus the maximum ranges recorded for Mount Tamalpais, Kentfield, and Hamilton Field are 19°100°, 17°-112°, and 27°-102°, respectively, while the mean temperatures for January and July for the same stations are: Mount Tamalpais, 43.7° (Jan.), 69.0°

L I F E ZONES AND PLANT ASSOCIATIONS

5

(July); Kentfield, 45.8° (Jan.), 65.5° (July); and Hamilton Field, 47.6° (Jan.), 66.3° (July). For these three stations the average annual mean temperature is 55.0°, 56.4°, and 57.8°. While the average seasonal range of temperature for these three places is about 20° between summer and winter, there are places along the ocean where the range is less than 5°. Thus at Point Reyes, where the minimum and maximum are 27° and 98°, the average temperatures are 49.8° (Jan.), 53.7° (July), and 52.5° (annual). This is a good example of an isothermal climate which is rarely found on land and which is in marked contrast with the continental type of climate. Along the eastern boundary of California, across the Sierra Nevada and beyond the influence of the ocean, the averages for January and July may vary by as much as 45° and differences between minimum and maximum temperatures may approach 140°. While the average annual mean temperature varies but a few degrees for stations on the coast and in the interior of Marin County, the extremes in annual rainfall are much greater and differ markedly within a short distance. At Point Reyes the average is only 18 inches but at Point Reyes Station near the head of Tomales Bay it is 32 inches. At Kentfield and Hamilton Field the differences are even greater, 45 inches at the former and only 28 inches at the latter. T h e precipitation on the lee side of the San Rafael Hills and at Black Point is perhaps still less. T h e summer fogs that are prevalent along the coast are a departure from the usual character of Mediterranean climate, and the influence of the cool moist air is felt far inland, even beyond the point where the mists are still condensed and visible. Fogs aTe most frequent and persistent along the immediate coast; and, although high country like the Sausalito Hills, Mount Tamalpais, and Inverness Ridge are effective barriers controlling their inland movement, there is no part of Marin County to which they do not penetrate when most extensive. It is to the fog that Point Reyes owes its equable, albeit chilly, summer temperature—a climate which impressed Sir Francis Drake and the crew of the Golden Hinde during their sojourn on the Point Reyes coast in June and July, 1579, as set forth in the notes of Chaplain Francis Fletcher in The World Encompassed. "During all which time, notwithstanding it was in the height of summer, and so neere the sunne, yet were wee continually visited with like nipping colds as we had [never] felt before" and by "those thicke mists and most stinking fogges." So impressed was the narrator by this unseemly summer weather that he devoted almost one-sixth of the account concerning the California visit to the cold and wind and to theorizing why the sun, even "in the pride of his heate," could not dissipate the "insufferable sharpnesse." All who have tried to explore the Point Reyes dunes and downs in the midst of a cold summer fog can fully sympathize with the early English visitors and even forgive them the slight exaggerations that color their record. L I F E Z O N E S AND P L A N T ASSOCIATIONS

There is so much difference in climate between the coastal and interior parts of Marin County that two life zones, as defined by C. Hart Merriam, can be recognized with the aid of plant indicators. On moister slopes and in canyons near the coast the Transition Zone is marked by such trees as Pinus muricata,

6

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FLORA

Pseudotsuga taxifolia, and Sequoia sempervirens, and also by many shrubs, among which are Corylus californica, Ribes Menziesii, Rubus parviflorus, Ceanothus tkrysiflorus, and Vaccinium ovatum. In this zone a large variety of herbaceous plants grow on open coastal slopes, in wooded canyons, or in meadows among the hills. This humid coastal belt gives way toward the interior to the Upper Sonoran Zone, which is represented by extensive grassland, usually by scattered oaks, and by chaparral on rocky, exposed ridges. These areas are relatively drier and may actually have less rainfall than the coastal districts, or the areas may be drier because of the steep slopes, rocky soil, windy or sunny exposures, or varying combinations of these features. In this zone the grassland and chaparral are usually evident enough, and the oaks, Quercus Douglasii and Q. lobata, may serve as useful zone indicators. Although the life zones are helpful in analyzing the flora of a region in a general way, particularly in an extensive area, the life-zone concept in Marin County is not so useful because conditions arising from the interaction of climate, topography, and substratum are extremely and locally varied. Within a short distance, conditions may change so completely that two entirely different groups of plants which are neighbors as far as space is concerned may be quite unrelated in their requirements of soil and moisture. Grassland may end abruptly on the edge of brush, forest may pass into chaparral, and dunes and salt marshes may adjoin one another. Varied physical conditions in a restricted area produce diverse expressions in the vegetation, and these can be best understood and appreciated by a consideration of the plant associations of the county. As is true in the defining of life zones, it is not always easy to limit or define a plant association; but in a general way this can be done satisfactorily enough, if due regard is given to the fact that nearly every plant association blends or merges gradually with one or more other associations which it may adjoin. Sometimes the intermediate area is narrow and scarcely noticeable, but at other times it may be quite extensive and may itself have a characteristic appearance. Gradual, rather than abrupt, change from one set of physical and biological conditions to another is largely responsible for this blending: it is in this intermediate zone where the plant communities are making their floristic readjustments as a new set of conditions is approached. T h e associations and the belt where they blend may be thought of as something more or less permanent and static, but usually this interrelationship of plant communities is a moving changeable thing that reflects in a vital way the response of the plants that make up the associations. Thus, in a landscape which constantly changes owing to geologic or other processes, new conditions are arising to which the plant communities respond; the development of the plant communities themselves creates conditions that modify the basic stability of the community as an organized entity; and natural or unnatural accidents (that may be catastrophic in relation to the plant association concerned) may occur at any time. So, while the plant communities are usually definite enough, they are not always stable, and intergradation from one to another is to be expected. In Marin County the following twelve associations can generally be distinguished: redwood forest, tanbark oak-madrono woodland, oak-buckeye woodland, Douglas fir forest, bishop pine forest, chaparral, coastal brush, grassland (sometimes closely related to one or another of these listed associations), streambank and

1. Redwoods (Sequoia sempervirens)

in M u i r Woods National Monument.

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