Field Guide to Mushrooms of Western North America

Field Guide to Mushrooms of Western North America

by R. Michael Davis, Robert Sommer, John A. Menge

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California and the Western States are rich in abundant and diverse species of mushrooms. Amateur mushroom collectors and mycologists alike will find over 300 species of the region’s most common, distinctive, and ecologically important mushrooms profiled in this comprehensive field guide. It provides the most up-to-date science on the role of fungi in the


California and the Western States are rich in abundant and diverse species of mushrooms. Amateur mushroom collectors and mycologists alike will find over 300 species of the region’s most common, distinctive, and ecologically important mushrooms profiled in this comprehensive field guide. It provides the most up-to-date science on the role of fungi in the natural world, methods to identify species, and locations of mushroom habitats. With excellent color illustrations showing top and side views of mushrooms of the Western States and a user-friendly text, it is informative but still light enough to be carried into the woods. When used to identify mushrooms, keys bring the reader to individual species, with a descriptive text providing cues for identifying additional species. Mushrooms common in urban landscapes are included, which is especially useful for the casual encounter with backyard fungi. The guide also provides a table of both old and new species names, and information on edibility and look-alikes, both dangerous and benign.

A section on mushroom arts and crafts features mushroom photography, painting, philately, spore prints, dyes, and cultivation. The guide also offers a comprehensive list of resources including national field guides, general mushroom books and periodicals, club and society contact information, and web sites.

· Primary descriptions and illustrations of 300 species of mushrooms plus text descriptions of many more.

· Latest word in mushroom taxonomy and nomenclature. Clear discussion of DNA sequencing and new classifications.

· Especially good coverage of southern California and Southwestern mushrooms often neglected in other field guides.

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University of California Press
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California Natural History Guides Series
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4.50(w) x 7.20(h) x 1.00(d)

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Field Guide to Mushrooms of Western North America

By R. Michael Davis, Robert Sommer, John A. Menge


Copyright © 2012 Regents of the University of California
All rights reserved.
ISBN: 978-0-520-27108-1



A mushroom is the fruiting body, or reproductive organ, of a fungus. Fungi are a unique group of organisms distinct from animals, plants, bacteria, and protozoa. Those fungi with fruiting bodies large enough to see and touch are the focus of this field guide. Fungi with microscopic fruiting bodies such as yeasts and molds receive mention here only as they relate to mushrooms. Slime molds, which are related to simple protozoan organisms, are covered briefly in this book because they share some characteristics with fungi.

Fungi consist of masses of microscopic, interwoven, and interconnected filaments individually known as hyphae and in mass called a mycelium. The mycelium of a mushroom-producing fungus usually remains out of sight underground or embedded in its substrate. Thus, a specific fungus may fruit year after year in the same place from the same mycelial body.

Unlike green plants, fungi do not possess chlorophyll and cannot produce their own food. Instead, they live on food originally produced by plants or animals. Threads of mycelium running through leaf litter on the forest floor, for example, form an extensive network that breaks down organic matter by excreting enzymes and then absorbing the carbohydrates, amino acids, vitamins, and other nutrients through the walls of the hyphae. Although it usually goes unnoticed, the mycelium of a single fungus can extend over acres of forest and reach several feet underground. Scientists have demonstrated that some fungi grow to gigantic proportions. In an eastern Oregon forest, a colony of Armillaria solidipes, which produces bundles of hyphae called rhizomorphs, was estimated to cover more than 2,000 acres. The weight of the colony may exceed 200 tons! If the colony is considered a single organism, then it is one of the largest if not the largest organism on Earth. When conditions are right, the fungus mycelium forms a knot that develops into a mushroom fruiting body. The fruiting body produces seedlike spores that serve as the reproductive units. A typical mushroom produces millions of spores dispersed by wind, water, insects, or animals to grow into mycelia at new locations.

Most of the fungi included in this field guide produce spores on one of two types of large, fleshy fruiting bodies. Members of the phylum Basidiomycota (loosely called basidiomycetes) typically produce four basidiospores on the outside of club-shaped microscopic cells called basidia (singular basidium). Members of the phylum Ascomycota (ascomycetes) produce ascospores, usually eight in number, inside thin, spherical to fingerlike sacs called asci (singular ascus). While the spore-bearing cells are microscopic, these two general groups of fungi often can be distinguished by the shape of the fruiting bodies. Fungi that have gills, teeth, tubes, pores, or spherical above-ground spore sacs are usually basidiomycetes, whereas fungi that are shaped like cups, saucers, or goblets are usually ascomycetes (see Figure 1).

Basidiomycetes have traditionally been classified based on the shape and structure of the fruiting body and especially the portion of the fruiting body that is lined with the basidia. Fruiting bodies may be erect, resupinate (lying flat against the substrate), shelflike, or effused-reflexed (partly shelflike and partly resupinate).

Genetic analyses have revealed that fruiting body shapes often are not good predictors of relationships among fungi. Nevertheless, for convenience we can categorize basidiomycetes based on their physical features for ease of identification. Thus, fungi that produce spores on platelike gills are called gilled mushrooms, and many that have pores or tubes, are soft and fleshy, and are shaped like mushrooms are known as boletes. Other fungi that are tough or woody with spore-bearing tubes or pores are called polypores. Fungi with downward-pointed teeth are known as tooth fungi. Others that bear spores on upright simple or branched fruiting bodies resembling erect clubs or corals are called club fungi and coral fungi. Fungi that produce spores inside an enclosed spherical structure are known as puffballs and earthstars.

Some ascomycetes bear their spores inside tiny, hollow, flask-shaped structures. These spore-bearing flasks are often clustered within a larger mass of rigid mycelia called a stroma. In the cup fungi the spore-bearing surface (hymenium) lines the inside of a cup- or saucer-shaped fruiting body. Asci are therefore directly exposed to the outside environment. In the subterranean truffles, the spore-bearing surface may be greatly convoluted as it lines labyrinthine-like folds inside the fruiting body. In other cases, ascus-lined cups have fused together in complex caps, as in the morels.

In a typical basidiomycete fruiting body, the mushroom fundamentally consists of a cap, gills, and a stalk (see Figure 2). The cap protects gills lined with the hymenium. When a mushroom is young, in the button stage, the cap often curves downward and inward against the stalk. This protects the cap against breaking as it pushes upward through the soil.

As a mushroom matures, the cap opens like an umbrella. The shape assumed by the mature cap is characteristic for a particular species. Caps may be hemispherical, convex, umbonate, conical, flattened, urn shaped, and so forth (see Figure 3), and may be smooth, pitted, wrinkled, or striate (radially lined). Stalks may be equal (with parallel sides), tapered toward the top or base, club shaped, bulbous, wiry, or hairlike, and short, long, central, eccentric (off-center), lateral (attached to the side of the cap), or absent. Some are reticulate (resembling a mesh netting stretched over the stalk).

Gills are a series of thin plates radiating from the stalk to the underside of the cap margin. The spacing between gills and their manner of attachment to the stalk are important taxonomic characteristics. Gill spacing can be divided into four categories: distant, subdistant, close, and crowded. Gill attachment to the stalk is described by the terms free, adnate, adnexed, notched, and decurrent (see Figure 4). All gilled mushrooms have full-length gills that extend from the edge of the cap to the stalk. Some species have additional short gills that extend from the cap margin and partway to the stalk.

Many mushrooms have protective structures known as veils. The universal veil or outer veil is a protective tissue that envelops the young mushrooms of some species. The veil breaks when the stalk elongates and the cap opens. Remnants of the veil left on the lower part of the stalk form a cup or volva, or may remain on the cap surface as patches or warts.

The surest way to determine if a particular species has a universal veil is to examine a young mushroom. If this is not possible, the mature mushroom must be carefully examined for veil remnants. A partial veil extends from the edge of the cap to partway down the stalk, protecting the hymenium when the mushroom is young. As the mushroom cap expands, the partial veil leaves remnants on the stalk, the cap margin, or both. A stalk that has remnants of the partial veil is said to have a ring or annulus. Veils are often like a membrane or sheet (membranous), but sometimes they are thin and ephemeral.

Some cap surfaces are dry, whereas others are viscid or slimy. The cap must be moist to detect a viscid surface, so if a fruiting body is dry, you may need to rub water on it. Clues that a fruiting body is viscid include the presence of a shiny lacquer or adhering leaves and other debris.

Color is one of the most conspicuous characteristics of fungi and can vary tremendously within a species. Russula cremoricolor, for example, can be red, yellow, or pink, whereas R. bicolor is a combination of various shades of pink and yellow. Some of these color variations may be due to changes that take place as the fruiting body ages, but some variations are governed by genetics. The color of fruiting bodies also can be influenced by the environment. Sunlight especially can affect color: if a fruiting body grows in the shade or under leaves, it may be pale relative to its normal color; conversely, fruiting bodies that grow in full sun may become "sunburned" and develop abnormal shades of color. In addition, heavy rains may wash out colors, and freezing and thawing can radically affect mushroom appearance. In some species, the moisture in a mushroom cap affects its color. A mushroom cap that becomes lighter as moisture evaporates from the flesh is called hygrophanous. Some caps are partially translucent when moist, allowing the gills to show through the cap, especially near the margin where the flesh is thinnest. Color changes or staining may occur in age or when fungal tissue is bruised or cut. Injured tissue may change color almost instantaneously, or the changes may become evident after several minutes or hours.

Odor is an important and often highly specific characteristic of many fungi. Some odors attract insects and animals to aid in the dissemination of spores. Truffles, for example, use their powerful odors to attract animals that will dig them up. Stinkhorns use their strong foul scent to attract insects that will carry away their spores. Sometimes, you may need to crush a specimen to release an odor. It is best to use fresh specimens, because aging specimens often lose odors or develop odors of decay.

Like odor, taste is sometimes used to identify specific fungi. Typical tastes are classified as mild, sweet, bitter, or acrid (peppery). Only taste specimens in groups known to be nonpoisonous. When in doubt, don't taste it. To assess the taste of a fungus, place a small piece of cap and gills on the end of your tongue before spitting it out. Many tastes are slow to develop. Use only fresh specimens, because some tastes may be associated with aging or decay.

Spore color is one of the first characteristics needed for mushroom identification. To determine spore color, you need a mass of spores because a single spore is microscopic (see p. 20 for instructions on making a spore print). Other spore traits, such as size, shape, and ornamentation, are important characteristics used to identify some species but are not stressed in this field guide because they require microscopic examination. Some of the common terms used to describe spore ornamentation are smooth, spiny, warted, ridged, or reticulate (intersecting ridges resembling a honeycomb). Often the spores react to certain chemicals. By far the most useful of these chemicals is iodine (Melzer's reagent). It is naturally reddish brown in color but turns bluish in the presence of starch, called an amyloid reaction.

Cystidia are microscopic end cells of various shapes that often have great taxonomic importance. In some species, they are covered with crystalline material or encrusted with other substances. Others have oily or refractive inclusions. Cystidia may occur on gill edges, on the sides of gills, on the stalk, or on the cap cuticle (pileocystidia).

For field identification, there is no substitute for experience. Keep notes on mushrooms you identify and you'll soon start recognizing patterns in color, shapes, and habitats. Become familiar with basic fruiting body architecture, such as the types and variations in veils, so you can quickly categorize certain groups of species. And don't forget the importance of spore color. This guide, as well as most other guides, uses spore color as one of the first steps toward identification.



Most fungi can be placed into one of three ecological categories according to the way they obtain their nutritional requirements: saprobic, parasitic, and mycorrhizal. Saprobic fungi absorb nutrients from plant litter, wood, dung, and so on. The process of decomposition breaks down organic matter and recycles nutrients, essential functions for the web of life. How wood is decomposed is a useful taxonomic characteristic. White rot fungi decompose both the lignin and cellulose of wood, leaving behind white residual cellulose in the partially decomposed wood. Brown rot fungi, in contrast, decompose the cellulose and leave the lignin intact, resulting in a rot characterized by small brown cubes of wood. Wood rot fungi help produce humus, which is critical for soil structure and growth of plants. Some fungi break down lawn thatch, growing from a center point and fruiting in fairy rings. The lawn at the growing margin is greener than the rest of the lawn because the fungus creates a flush of nutrients as it decomposes organic matter.

Parasitic fungi extract nutrients from living plants, resulting in plant disease and sometimes plant death. Some cause billions of dollars in losses to farmers and foresters. Notable examples are Armillaria root rot, the cause of extensive economic losses to ornamental trees, fruit and nut production, and the timber industry; Dutch elm disease, which has devastated elm trees across the United States; white pine blister rust; and late blight, which caused the Irish potato famine in the mid-1800s and continues to plague potato production today. Sudden oak death, caused by the funguslike organism Phytophthora ramorum, is a serious disease of oaks and other plants of the Pacific Northwest and California.

Mycorrhizal fungi grow in a symbiotic, mutually beneficial relationship with plants. The name mycorrhiza is derived from the Greek myco, meaning fungus, and rhiza, or root. The mycelium penetrates the plant's roots and forms a protective sheath around them. The mycelium radiates from the mycorrhizal roots and explores the soil. This mycelial network greatly increases the absorptive surface area of the root and mines the soil for nutrients such as phosphorus, zinc, copper, potassium, and nitrogen, which it passes to the host plant. Because of this symbiotic relationship, many trees can grow and prosper in extremely poor soils. In return, the host tree provides the fungus with carbohydrates, amino acids, and vitamins, which may be the fungus's sole food supply. Without these mycorrhizal associations, pines, firs, manzanitas, oaks, aspens, birch, and many other tree species would struggle to survive. These forests provide collectors a bounty of mycorrhizal mushrooms.

Although a single mushroom cap may release millions of spores, few spores arrive on a suitable substrate at the right time to germinate and successfully compete for nutrients. Thin-walled and nonpigmented spores are easily damaged by ultraviolet light and desiccation and cannot survive long-distance travel. Because much higher concentrations of spores arrive near the parent fungus, fungi often become somewhat localized. When spores arrive on a suitable substrate, they may germinate and produce hyphae, but only a mycelium generated from two spores of different mating types can produce fruiting bodies. Fungal mating types are not like the "male" and "female" system in animals, with only a 50 percent rate of sexual compatibility. Instead, there may be large numbers of mating types, most of which are sexually compatible. However, the spores from one fruiting body usually have limited sexual compatibility, which discourages inbreeding and promotes outbreeding, providing genetic diversity, and hence adaptive ability.

Fungi often become localized because of habitat specificity and precise requirements for moisture and temperature. Due to the arid climate of much of the western United States, a large number of western fungi have evolved mechanisms to cope with drought. Indeed, climate is a driving force for the evolution of our unique fungal flora. Truffles, for example, have developed a subterranean existence where moisture levels are more consistent and manageable. These fungi require external agents such as animals and insects to spread their spores. Other fungi have adapted to drought conditions by allowing their fruiting bodies to dry out and then quickly rehydrate during rare rain events. Some Marasmius species, jelly fungi, and many of the crust fungi fall into this category. Still others manage by growing under logs or remaining under the litter layer and producing "shrumps" (mushroom humps). This conserves moisture and allows spores to be released even during relatively dry periods. Many fungi, such as puffballs and bird's nest fungi (e.g., Nidula candida), are adapted for rain dissemination and release their spores only when abundant moisture is present. Others, such as Podaxis pistillaris, a common desert and chaparral fungus, produce thick-walled dark spores that are well suited to survive long periods of drought, sun, and heat.


Excerpted from Field Guide to Mushrooms of Western North America by R. Michael Davis, Robert Sommer, John A. Menge. Copyright © 2012 Regents of the University of California. Excerpted by permission of UNIVERSITY OF CALIFORNIA PRESS.
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Meet the Author

R. Michael Davis is Professor of Plant Pathology at University of California, Davis. Robert Sommer is Distinguished Professor of Psychology Emeritus at University of California, Davis, and the author of Personal Space and Tight Spaces, among other books. John A. Menge is Professor Emeritus of Plant Pathology at University of California, Riverside.

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