Most tricholomas are relatively large showy mushrooms that draw attention from mushroom hunters, nature lovers, and casual forest walkers alike. Although only a few of them are popular edibles, tricholomas have great ecological importance due to their mycorrhizal associations with many of the dominant temperate forest tree species.
Unfortunately, when it comes to naming them, probably every North American field mycologist has struggled with the identification of Tricholoma species. By and large, the greatest obstacle has been a lack of readily available reference materials, especially those having illustrations in color, which are particularly valuable for distinguishing many tricholomas that are otherwise similar in size, stature, and other morphological characters. In addition, until now there has been no reasonably comprehensive treatment of the North American species. Popular mushroom guidebooks typically feature only a small number of the more common tricholomas that are encountered, and the technical literature is scattered, often difficult to obtain, and can be daunting to those not formally trained in mycology.
Currently, it is not possible to provide complete or entirely definitive coverage of Tricholoma for a number of reasons. For one, compared to the situation in Europe, North American mushrooms are poorly known and nearly all groups are in need of much additional study. Unfortunately few studies are being conducted, as almost no funding is available to support them. Instead, the small number of North American systematic mycologists are more likely to be funded to study the mushrooms of other places. For another, mushroom taxonomy in general is in a state of rapid flux, due primarily to the impact of DNA sequencing and computerized phylogenetic analysis, and this is likely to continue for the foreseeable future.
Thus, we recognize that this book represents only a first effort to describe and illustrate the tricholomas of North America and that it unavoidably will contain information that will require revision in the future. However, we look at it in much the same way that U.S. soil scientists viewed their initial efforts to classify our nation’s soils. The first published classification was called an “approximation” and, as information and understanding grew, it was replaced by six more "approximations." Over 25 years passed before Soil Taxonomy was deemed ready to be issued without the tag of “approximation.” Hopefully, publication of this book will spur increased study of this interesting and important group of mushrooms and represent a first approximation to a future monograph of North American tricholomas.
Our goal is to provide a means to identify the majority of North American tricholomas within the context of the current system of names and classification. Because of the disparity of knowledge of the mushrooms that inhabit different parts of the continent, our coverage focuses primarily on the United States and adjacent parts of Canada and much less on Mexico and northern Canada, where much less information is available. Nonetheless, we believe this book provides a valuable compilation of information and fills the gap between technical publications and the limited representation of tricholomas in North American mushroom field guides. Even if some of the information presented here fails to survive future revisions of Tricholoma classification and nomenclature, we feel the descriptions and especially the color images will have lasting value. We have selected the best documentary photos available from our own extensive collections, and augmented them with images graciously contributed by many of our fellow mushroom photographers. Whenever possible, we have included more than one image of a species to illustrate the wide variation exhibited by many tricholomas.
It is our hope that, even with some unavoidable limitations, this book will be an important addition to the mycological literature and that it will serve its users well.
Introduction to Tricholoma (Fries) Staude
More than 100 species of Tricholoma have been reported from North America. They are often referred to as trichs (pronounced either “tricks” or “trikes”), although some field guides call them cavaliers or knights. Most are relatively large and fleshy mushrooms, and some are rather colorful. Thus, they represent a conspicuous element of our mycota. Tricholomas grow on the ground near certain types of trees and typically fruit from late summer through early winter or even into spring in warmer areas. A few of them are fine edibles, while others are inedible or even poisonous. However, the edibility of the majority of tricholomas is not well known. Thus, great care should be taken by anyone inclined to consume any of them. As with any wild mushrooms gathered for food, positive identification is essential.
The Genus Tricholoma
What we know as the genus Tricholoma originated with Elias Magnus Fries in his 1821–1828 publication, Systema Mycologicum. In this early version of Fries’s classification system, Tricholoma constituted one of 36 tribes (Tribe V) within the huge genus, Agaricus, which included nearly all of the gilled mushrooms.
Fries defined Tricholoma as including fungi that produce white-spored terrestrial mushrooms that are fleshy and relatively robust. They lack a universal veil (so there is no volva on the stalk base or warts/patches on the cap) and either lack a partial veil or have one that is fibrillose or floccose and disappears early, sometimes leaving remnants on the margin of the cap. The cap is hemispherical or somewhat bell shaped with a thin incurved (at least when young) margin. The gills are of unequal length and emarginate or rounded where they approach the stalk. The stalk is not smooth, but rather is fibrillose, scaly, or has coarse longitudinal striations formed by aggregated fibrils, and its flesh is confluent with that of the cap. The mushrooms exhibit diverse colors. Including additions in his later publications, Fries’s Tricholoma eventually included over 100 species.
The name Tricholoma is derived from two Greek roots—tricho = hair and loma = fringe—referring to the fibrillose partial veil remnants found on the cap margin in several species. Interestingly, however, most tricholomas do not exhibit this feature.
Another of Fries’s tribes—Tribe III, Armillaria—is also important in the history of Tricholoma. The principal difference between Fries’s armillarias and tricholomas is the existence in the former of a membranous partial veil that leaves a ring on the stalk. Not surprisingly, over time, taxonomists have done a lot of shuttling of species between Armillaria and Tricholoma, such that now a number of the Friesian armillarias reside in Tricholoma.
Since 1972, Tricholoma has been considered to have become a genus in 1857 with the publication of Friedrich Staude’s Die Schwämme Mitteldeutschlands insbesondere des Herzogthurms. The decision to designate Staude as the authority for the genus was not without controversy, as some mycologists felt that Paul Kummer (Der Führer in die Pilzkunde), who had been designated the authority in 1953, was more appropriate. Still others favored the selection of Lucién Quélet (Champignons du Jura et des Vosges). Thus, each of those names appears as the authority in various publications.
The type species for the genus is Tricholoma flavovirens (Persoon) S. Lundell, which currently is thought to represent the same species as T. equestre (Linnaeus) P. Kummer. A recent analysis concluded that if the two names are in fact synonyms, then T. equestre should be used because it is the earlier of the two.
Following Fries’s initial definition of Tricholoma, mushrooms continued to be collected and examined, and new technologies, such as microscopes, were employed, which allowed previously unrecognized features of mushrooms to be observed. This resulted in some Friesian tricholomas being transferred to other existing genera and others providing the basis for defining new segregate genera. Thus, some former tricholomas became members of Calocybe, Dermoloma, Lepista/Rhodopaxillus, Leucopaxillus, Lyophyllum, Melanoleuca, Porpoloma, Rhodocybe, Tephrocybe, Tricholomopsis, and Tricholosporum. Because many of the mushrooms in these genera share the essential macroscopic features of Tricholoma, they can cause confusion and produce identification challenges for mushroom hunters.
Current Concept of Tricholoma
The current concept of Tricholoma differs little from Fries’s view of it—fleshy terrestrial mushrooms with a white spore-print, smooth, inamyloid spores, parallel gill trama, and (mostly) emarginate or sinuate gill attachment. However, because the concept now is based in part on microscopic features (or their absence), it is not always possible to be certain that you have a tricholoma without using a microscope.
Many white-spored genera include species that could be mistaken for a tricholoma. Although it isn’t possible to list every genus that someone might consider to be a tricholoma “look-alike,” the following are the more likely ones. The descriptions include only the key features for distinguishing them from tricholomas.
Amanita—universal veil present, leaving a volva on the stalk base, and often warts or patches on the cap; skirt-like ring often present; gills free or nearly so, often seceding. Cap margin often striate. Most have an elegant gestalt, not easily described, but readily appreciated with a bit of experience.
Armillaria (the honey mushrooms, formerly Armillariella)—usually found on wood, often in clusters, tough black rhizomorphs often present in substrate, the typical honey colors of their fruitbodies are rare or absent in tricholomas, gills adnate to decurrent.
Calocybe—white or brightly colored fruitbodies, basidia contain siderophilous granules, spores sometimes roughened, cap cuticle sometimes cellular.
Catathelasma—large, hard-textured mushrooms, adnate to decurrent gills, stalk tapered downward and with double ring, amyloid spores.
Clitocybe—gills usually decurrent and fruitbodies often funnel-shaped, at least at maturity.
Collybia sensu lato (including Gymnopus and Rhodocollybia)—cap margin incurved to inrolled (at least when young), stalk with a cartilaginous rind, gills adnexed to adnate, spores usually pinkish in Rhodocollybia.
Dermoloma—smallish fruitbodies, cap cuticle hymeniform (filamentous in tricholomas), spores amyloid in some species.
Floccularia—spores amyloid, stalks typically floccose, usually with a membranous ring.
Hygrophorus (sensu stricto—the medium to large, mostly dull-colored species)—gills thick and waxy-looking, adnate to decurrent, gill trama divergent.
Laccaria—fruitbodies with distinctive orange-brown, pinkish brown, or purplish colors that are rare or absent in tricholomas, gills thick and waxy-looking, usually pinkish brown, lilac, or purple, stalk rather tough and fibrous, spores roughened to spiny and often nearly spherical.
Lepista—spore-print with pinkish tones, spores roughened.
Leucopaxillus—abundant mycelial cords or mat often present at base of stalk, fruitbodies often very firm and slow to rot, spores amyloid, sometimes roughened.
Lyophyllum (including Tephrocybe)—basidia contain siderophilous granules, fruitbodies usually dull colored and often with greasy appearance, many species stain black.
Megacollybia—usually found on wood, gills rather broad, their edges with abundant cystidia.
Melanoleuca—cap hygrophanous and often broad relative to stalk length, spores amyloid, roughened, gills usually with abundant cystidia.
Porpoloma—spores amyloid, gill edges typically with cystidia.
Tricholomopsis—usually found on wood, often bright yellowish, gill edges often with abundant cystidia.
Tricholosporum—spores angular, or shaped like crosses.
In addition to these pale-spored genera, many species of Entoloma (sensu stricto) and Hebeloma have the same stature as a typical tricholoma. However, they are easily recognized by their salmon / pinkish brown and dull brown spores, respectively. Small brownish tricholomas can appear very much like species of Inocybe but, again, spore-color (brown in inocybes) quickly separates them.
Subdivision of Tricholoma
The genus, Tricholoma, has been divided into subgroups since its creation. In Systema Mycologicum (1821), Fries recognized four groups based on the nature of the cap surface. In Epicrisis Systematis Mycologici (1836–1838), he recognized seven groups, mostly based on the nature of the cap surface, but also including consideration of such things as season of occurrence and the fleshiness, fragility, and shape of the cap. Each of these groups was then divided further based on color, width of the gills, and discoloration of the gills. For the most part, Fries retained this latter classification in his later works, although he did make minor revisions, changed some names, and moved some species around.
Most mycologists of the late 1800s and early 1900s, including Charles Horton Peck and C. H. Kauffman in the United States, divided the genus in ways very similar to Fries’s scheme. Additional macroscopic features such as odor, taste, size, and color were utilized in many of these groupings. Of course, as genus definitions evolved and species were moved (mostly) out of Tricholoma, the changing species composition of the genus was reflected in its subdivision. In parallel with the new genus alignments based on macroscopic features, the subdivision of Tricholoma also began to reflect microscopic features, such as the presence of clamp connections, anatomy of the cap cuticle, and location of pigments in the colored species (within the hyphae versus encrusting them).
Perhaps the two most widely used subdivisions of the genus are those by Marcel Bon and Rolf Singer. However, we chose not to utilize formal subdivisions of the genus for this book because: there is no one widely accepted scheme for doing so; many of the features used to define subgroups are gradational and not always easy to apply, hence Kauffman’s observation that, “The grouping of this large genus is fraught with considerable difficulties.”; the existing schemes are likely to be revised substantially, or even replaced, as the results of molecular studies and morphological-molecular integration lead to increased understanding of the evolutionary relationships within the group; and, most of all, we don’t feel including one of the existing subdivision schemes would add significantly to readers’ ability to identify North American tricholomas. For those who are interested in this level of detail, we suggest reviewing the publications by Bon, Kauffman, Ovrebo, Shanks, and Singer.
History of the Study of Tricholoma in North America
Despite the fact that tricholomas are among the larger and more conspicuous of our woodland fungi, the genus historically has received very little attention in North America.
Charles Horton Peck described over 60 Tricholoma species in the late 1800s and early 1900s, although many of them later were transferred to other genera. In what still is the only comprehensive treatment of the genus in North America, William Alphonso Murrill prepared the “Tricholoma” section of the North American Flora, under the genus names Melanoleuca and Cortinellus. Thus, many non-tricholomas were included in Murrill’s compilation.
C. H. Kauffman’s Agaricaceae of Michigan included an extensive treatment of the tricholomas of the Great Lakes region. During his prolific career, Alexander Smith of course studied the genus and described a number of species. However, he did not deal with it in a comprehensive fashion.
Probably the most active North American student of Tricholoma over the past few decades has been Clark Ovrebo. His master's thesis dealt with the tricholomas of the Pacific Northwest and his PhD dissertation covered the tricholomas of the Great Lakes region. Since completing his graduate studies, Dr. Ovrebo has continued work on the genus and has published a number of articles, describing new species and clarifying some of Peck’s species concepts.
Kris Shanks surveyed the tricholomas of California for her master's degree and later published the bulk of her thesis as a fascicle of the Agaricales of California series.
A number of other mycologists, including Tim Baroni, Howard Bigelow, Roy Halling, and Scott Redhead, have made contributions to our knowledge of Tricholoma in North America. In addition, amateur mycologists have helped expand our understanding in areas such as the northeastern United States, southeastern Canada, and the Pacific Northwest.
It is our hope that publication of this book will encourage further studies of Tricholoma in North America and elsewhere, as there still is much to learn.
Ecology of Tricholomas
Tricholomas all are believed to be ectomycorrhizal, forming a nutritionally reciprocal association with certain trees, shrubs, and possibly even some herbaceous plants. Thus, they are almost always found where trees are present—most often in forests and parks. Many trees, both hardwoods and conifers, are known to partner with tricholomas, including oak, beech, birch, willow, aspen, cottonwood/poplar, pine, spruce, fir, hemlock, and Douglas-fir. When found beneath isolated trees or in more or less pure stands, the association is fairly obvious, while in mixed woodlands containing a variety of ectomycorrhiza-forming trees, it can be more difficult to determine a specific relationship. However, although much remains to be learned about the specificity of mycorrhizal associations between tricholomas and host trees, knowing which species of tree the subject mushrooms were growing with can be critical for identifying them. At a minimum, it is important to know whether the nearby trees were conifers or hardwoods, and so this information should always be included in your field notes.
Edibility of Tricholomas
The genus Tricholoma consists mostly of relatively large fleshy mushrooms, some of which are common and often abundant. Because of this, they are likely to attract the attention of those who collect wild mushrooms for food. However tempting they may appear, relatively few members of the genus are known to be particularly good edibles. The edibility of many species is unknown, some are decidedly toxic, and one has proven deadly under certain circumstances. Add to this that edible tricholomas can be difficult to distinguish from those that are suspect or poisonous, and it becomes clear why they are not widely gathered for the table.
There are exceptions such as the highly prized American matsutake (T. magnivelare), which some consider to be among the best of all edible wild mushrooms. Our matsutake is a close relative of the Japanese species (T. matsutake). Both are highly esteemed and can command steep prices in commercial markets. However, not everyone rates matsutake at the top of his/her list of edible wild mushrooms, especially on first tasting it. For many, its unique flavor may be an acquired taste. In Japan, matsutake has considerable cultural significance and its almost reverent adoration stems partly from centuries of tradition. As availability of native matsutake has been declining in Japan, demand there for the American version has created a lucrative market that supports widespread commercial harvesting of the species in British Columbia, other parts of the Pacific Northwest, and, more recently, Mexico.
Tricholoma portentosum is a widely distributed edible that, particularly in the East, can be quite common beneath pines from late fall to early winter, or later in the deep South. It is appreciated both for its flavor and availability well after most other edible wild mushrooms have finished fruiting for the season.
Tricholoma terreum is a popular edible mushroom in Europe where it is commonly available in markets, both fresh and canned. Although the name “T. terreum” appears in many North American field guides and we have included it in this book, it is not clear whether that species actually occurs here, or whether we are misapplying the name to one or more different species. In any event, what has been referred to as T. terreum is not popular in North America, in large part because it is similar to several possibly poisonous species and one must learn to confidently recognize it. Although small for a tricholoma, it often grows in large groups and then can be collected in quantity.
The gastronomic quality of Tricholoma caligatum has received mixed reviews, being described as everything from very good to disgustingly inedible. We have sampled this species a number of times in New York, West Virginia, North Carolina, and Florida and, until recently, had always found it to be intensely bitter and/or acrid and unpalatable. However, a collection made in Florida while this book was in preparation proved mild and palatable. Bitterness and inedibility also has been the typical experience in the Pacific Northwest. However, there are also reports, from the southern Rocky Mountains for instance, of it being an excellent edible. Tricholoma caligatum is considered a highly variable species, so perhaps there is more than one species going by that name, or it may be that different populations differ in their palatability. It also is possible that at least some of the edible collections of T. caligatum actually are matsutake, T. magnivelare. Until more is known about the reason(s) for the inconsistent edibility of this mushroom, we recommend caution when trying it.
There are a number of other tricholomas that are reported to be edible either in North America or Europe, but with which we have little or no first-hand experience. Examples include T. atrosquamosum, T. orirubens, T. populinum, T. scalpturatum, and T. subresplendens / T. columbetta.
Fortunately, no tricholoma of which we are aware is dangerously poisonous when sampled in small amounts. However, no discussion of their edibility would be complete without addressing T. equestre / flavovirens. At one time, both in North America and Europe, this seemingly widespread mushroom was regarded by many as the best edible in the genus (especially when matsutake was classified as Armillaria), and it has a long history of use in many parts of the world. However, in 2001, the New England Journal of Medicine reported a dozen cases of poisoning, including three fatalities, that occurred in France, all following consumption of several consecutive meals that included large amounts of T. equestre / flavovirens. The victims experienced severe rhabdomyolysis, a disease that destroys muscle tissue. Similar poisonings also have been reported from Poland. For many years, we have enjoyed eating this mushroom with no ill effects and this has been the experience of many other mushroom eaters throughout North America. Nothing resembling the European incidents has been reported here. Despite this clean record, we no longer eat T. equestre, and we cannot recommend its use until further research clarifies the reasons behind the puzzling occurrence of the European poisonings, or demonstrates that our North American species is different from the toxic European one. At a minimum, one should not eat large amounts of this or any other mushroom repeatedly over a short (on the order of a few days) time.
Macroscopic Features Used for Identifying Tricholomas
Identification of tricholomas relies heavily on size of the fruitbody and macroscopic features of the cap such as color, the presence or absence of scales or radiating fibrils on the surface, and whether it is dry, moist, or viscid. Odor and/or taste of the flesh is sometimes a defining character. The gills are white to off-white in most species but can also be grayish, buff, or yellow. Spotting, staining, or discoloring (often reddish brown) of the gills in age or after damage is a characteristic feature of many species.
Although gill attachment is rarely, if ever, used to help differentiate species within Tricholoma, it is an important character for recognizing the genus. Usually it is described as being emarginate, notched, or sinuate. Unfortunately, gill attachment can be a rather variable feature and these terms have been interpreted differently from mycologist to mycologist. C. H. Kauffman described the variability nearly a century ago:
Theoretically, they [the gills] are always emarginate behind, but this condition varies considerably. It is true that, in the mature plant, when the pileus is fully expanded, they become either sinuate or emarginate in most cases, although a single specimen may not always be normal in this respect. When young, however, they often do not show this character clearly, but are then adnexed, rounded-adnate, or adnate in such a way that they are merely a little less broad at the attached portion than they are a few millimeters from the stem, and this short distance is often marked by a straight edge rather than a rounded edge. . . . In old stages the gills may even become spuriously decurrent.
Thus, when attempting to determine the gill attachment of a putative tricholoma, it is best to examine multiple specimens of different ages and to allow for some latitude in interpretation.
Size of the fruitbodies can vary within a species and so exact measurements are not always useful. Thus in the keys, we have used small, medium, and large as follows, based on the diameter of the mature caps: small refers to caps with diameter usually less than 5 cm; medium to caps usually between 5 and 10 cm; and large to caps usually greater than 10 cm. The stalk is usually more or less equal but may be swollen in the middle (ventricose), tapered downward, or enlarged to slightly bulbous at the base. It is fleshy or fibrous like the cap and can be solid, stuffed, or hollow. Its surface usually is dry and longitudinally striate, but also can be nearly smooth, appressed-fibrillose, scaly, or slightly scurfy (at the apex only). Stalk color often is white, but it may be tinged with the cap color, or, more rarely, fully concolorous with the cap. Staining from bruising, handling, or with age is sometimes important in distinguishing between species. A number of tricholomas have a cortina. In these species, the veil often is delicate and fleeting, and may be visible only on very young specimens, leaving just a trace of fibrils as a faint ring-zone on the upper portion of the stalk or a fringed margin on the cap. A few species have a more substantial membranous veil that leaves a more or less prominent ring on the stalk.
Common odors of tricholomas include farinaceous, cucumber, coal tar, and, of course, the matsutake’s cinnamon-Red-Hots-with-old-gym-socks aroma. In many cases, the odor is pleasant, although not easily describable, and we have referred to these as being fragrant. The more common tastes are mild, bitter, and farinaceous.
Color-change reactions following the application of chemicals to the fruitbody (macrochemical reactions) are not used widely in identifying tricholomas, but they can be important in some cases. Potassium hydroxide (KOH), ammonium hydroxide (NH4OH), and paradimethylaminobenzaldehyde (PDAB) are of most use.
Microscopic Features Used for Identifying Tricholomas
Microscopic features are important for distinguishing the genus Tricholoma from other genera that are similar macroscopically (see Current Concept of Tricholoma [p. 000]), and they also are of use in separating species within Tricholoma. However, although the shape and size of spores and cystidia, the presence of clamp connections, and the structure of the cap cuticle sometimes are of value, microscopic features generally are less distinctive, less variable, and less helpful for distinguishing species in Tricholoma than they are in many other genera. Consequently, our species descriptions include only those microscopic features that seem critical for identifying the species in question. Spore size and shape are given for every species. Cheilocystidia, pleurocystidia, clamp connections, and pseudoparenchymatous hypodermium are mentioned when they are present. For those seeking more complete information about microscopic characters, we recommend consulting the works listed in the References section.
Notes on the Descriptions of Species
Each description consists of the following components.
Scientific name: The Latin binomial is provided for each species. We have tried to use the currently most widely accepted names, usually following the listing in Index Fungorum. Thus, the name used here might not be the same one found in other guides. In cases where this involves a shift from a widely recognized name, we have included the former name in our comments. The scientific name also includes the author citation, for the convenience of readers who are interested in the origin of the species concept and name. In some instances, the author citation is simple. For example, the entry "Tricholoma muricatum Shanks" indicates that this species was described and named by Kris Shanks. Sometimes, however, the original author’s name is enclosed in parentheses and followed by the name of the person who later reclassified the mushroom. For example, "Tricholoma magnivelare (Peck) Redhead" was originally described by Charles Peck as Agaricus magnivelaris and later transferred to Tricholoma by Scott Redhead.
Common name: One or more common names are provided in cases where we felt their usage was reasonably widespread and well established, or otherwise desirable. To reduce confusion, we used trich consistently as the base name, rather than cavalier or knight. In addition to common names that have appeared in other guides, we coined a few new common names where we thought this would be useful to some readers.
Cap: Information about the size and shape of the cap, its disc and margin, surface texture, and color is provided.
Flesh: The thickness, texture, color, and staining reaction when exposed are described in this section. Some tricholomas have distinctive odors and tastes (although often these are not easily describable in terms on which everyone would agree), and this information is noted whenever possible. It is important to remember that some mushrooms, including some tricholomas, taste hot and peppery and may irritate, burn, or numb your mouth if chewed for an extended period. However, there is negligible risk in properly tasting mushrooms. To taste mushrooms safely, place a small piece (no greater than the size of a small garden pea) on the tip of your tongue, chew it with your front teeth for a few seconds, and spit it out. If the taste initially is mild (not bitter, peppery, astringent, etc.), wait a minute and then chew a second small piece for 15 to 30 seconds before spitting it out. The tastes of some mushrooms are subtle or take time to develop.
Gills: Attachment, width, spacing, color, bruising reactions, and additional features of the faces or edges are noted.
Stalk: Information about the length, thickness, shape, texture, color, staining reactions, whether it is solid, stuffed, or hollow, and nature of the ring, when present, is provided.
Microscopic features: Information about spore size and shape is presented here. Additional microscopic features, such as cap cuticle structure and cystidia, are described when present and distinctive.
Occurrence: The habit (e.g., solitary, scattered, in groups or clusters), substrate, habitat, known or likely distribution, and commonness are described here. The usual fruiting period for many tricholomas is mid to late fall. However, their season extends later in areas such as California and the Gulf Coast, so typical “fall” species may appear there well into late winter or early spring. Commonness usually is described in terms of the overall distribution, and it can be expected that the descriptor will not be equally accurate in all parts of the species’s range. For instance, taxa listed as “occasional” may be quite common or locally abundant in some areas or years and rare or absent in others. However, at this time it is not possible to provide definitive information on distribution, frequency, and abundance of tricholomas because of the lack of data, historic confusion over the application of species concepts, and difficulty in identification.
Edibility: Species known to be edible are listed as such. We recommend that none of the other species be eaten. In addition, it is important to remember that even the best “edible” mushrooms are not equally edible for everyone—some persons are sickened by species that are tolerated by the vast majority of mushroom eaters. Thus, the precautions included in most mushroom guides should be observed, especially proceeding with moderation and caution until you know that a given species is edible for you.
Comments: This section includes synonyms, comparisons with similar species or varieties, the meaning of the species epithet, and other useful or interesting information about the species described.
A Note about Names
Mushroom systematics (naming, classifying, and study of their evolutionary relationships) is in a state of rapid flux. Analysis of the large amount of DNA-sequence and other molecular data being produced is leading to many changes in how we view the evolutionary relationships among mushroom fungi and, as a result, in their classification and names. Fortunately, Tricholoma has been affected much less by these developments (so far, at least) than many other mushroom groups, and so the impact on this book has not been great. Nonetheless, in our effort to use the most current names, some of the ones we’ve chosen might be unfamiliar to some North American mushroom hunters. Because name changes represent probably the biggest source of frustration for many mushroomers, where we have used a recent name we have also included the older, probably more familiar name in our comments and the index.
A bigger issue for this book comes from not knowing whether the North American fungi to which European names have been applied really do belong to the same species. Few, if any, mycologists have spent enough time on both continents to have first-hand comparative knowledge of large numbers of their respective fungi, and few critical studies have been done to evaluate our use of European names. The more comprehensive studies that have been done, which unfortunately do not include Tricholoma, suggest that many of our species are essentially the same as their European counterparts. However, for many others, our fungi do not quite fit the European concepts and thus probably should be given new names or have existing, but unused, North American names resurrected. Although this can be confusing, it results from the fact that mycologists are developing better understandings of the evolutionary relationships among the mushroom fungi.
Species Not Included in This Book
In reviewing the literature on North American tricholomas, we encountered a large number of names of species that have been used rarely, if at all, and others whose application here could not be readily confirmed. In cases where the concept of the species could be ascertained clearly from the original description and seemingly represented a valid species, we included it. However, for most rarely used names, the available information was not sufficient to clearly define the species concept and, in those cases, we decided to not include the species. We have provided a list of these and other excluded species following the species descriptions. The list includes European species reported to occur in North America, but whose occurrence we were unable to substantiate.