The Genus Tricholoma in North America Steve Trudell
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The Genus Tricholoma in North America Steve Trudell Note: Most of the material presented genus, Agaricus, which included nearly history of Tricholoma. The principal in this article has been taken, with all of the gilled mushrooms. difference between Fries’s armillarias modification, from Tricholomas of North Fries defined Tricholoma as including and tricholomas is the existence in America: A Mushroom Field Guide, by fungi that produce white-spored the former of a membranous partial Alan Bessette, Arleen Bessette, Bill Roody, terrestrial mushrooms that are fleshy veil that leaves a ring on the stalk. Not and Steve Trudell, newly published by the and relatively robust. They lack a surprisingly, over time, taxonomists have University of Texas Press. universal veil (so there is no volva on done a lot of shuttling of species between the stalk base or warts/patches on the Armillaria and Tricholoma, such that cap) and either lack a partial veil or now a number of the Friesian armillarias ost tricholomas are large have one that is fibrillose or floccose reside in Tricholoma. showy mushrooms that and disappears early, sometimes leaving Tricholoma is considered to have readily attract the attention of remnants on the margin of the cap. become a genus in 1857 with the Mmushroom hunters. Although only a few The cap is hemispherical to obtusely publication of Friedrich Staude’s are popular edibles, all tricholomas are flattened or, when young, somewhat Die Schwämme Mitteldeutschlands very important ecologically because of bell-shaped with a thin incurved insbesondere des Herzogthums Coburg. their ectomycorrhizal associations with margin. The gills are of unequal length However, Paul Kummer and Lucien many of the dominant temperate and and emarginate or rounded where they Quélet each appear as the genus boreal forest tree species. Unfortunately, approach the stalk. The stalk is not authority in some publications. The when it comes to naming them, probably smooth, but rather is fibrillose, scaly, type species for the genus is Tricholoma every North American field mycologist or has coarse longitudinal striations flavovirens (Persoon) S. Lundell, which has struggled with the identification of formed by aggregated fibrils, and currently is thought to represent the Tricholoma species and “Tricholoma sp.” its flesh is confluent with that of the same species as T. equestre (Linnaeus) is a common feature of foray displays cap. The mushrooms exhibit diverse P. Kummer. A recent analysis concluded and species lists. By and large, the colors. Including additions in his that, if the two names are in fact greatest obstacle has been a lack of later publications, Fries’s Tricholoma synonyms, then T. equestre should be readily available reference materials, eventually included over 100 species. used because it is the earlier of the two especially those having illustrations in The name, “tricholoma,” is derived (Deng and Yao, 2005). color, which is particularly valuable for from two Greek roots—tricho (thrix) The current concept of Tricholoma distinguishing many tricholomas that = hairy and loma = border or fringe— differs little from Fries’s view of it— are otherwise similar in size, stature, and referring to the fibrillose partial veil fleshy terrestrial mushrooms with a other morphological characters. remnants found on the cap margin in white spore-print, smooth, inamyloid Far more than 100 species of several species. Interestingly, however, spores, parallel gill trama, and (mostly) Tricholoma have been reported from most tricholomas do not exhibit this emarginate or sinuate gill attachment. North America, although the list of feature. The typical tricholoma stature features well documented taxa is much shorter. Another of Fries’s tribes—Tribe III, a broadly umbonate cap that is wide Tricholomas often are referred to as Armillaria—also is important in the relative to the length of the stalk and a trichs (pronounced either “tricks” or “trikes”), although some field guides call them cavaliers or knights. They 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 our tricholomas is not well known. Tricholoma (Fries) Staude What we know as the genus, Tricholoma, originated with Elias Magnus Fries in his 1821–1832 Fig. 1. Examples of gill attachment. Top row, left to right: free, adnexed, publication, Systema Mycologicum. In adnate. Bottom row, left to right: notched or sinuate, decurrent. Although this early version of Fries’s classification tricholomas typically have notched or sinuate gills, many will be found system, Tricholoma constituted one of 36 tribes (Tribe V) within the huge with adnexed gills, and some will even appear to be free. Illustration by Marsha Mello. Winter 2012 • Volume 5:5 • FUNGI 23 of different ages and to allow for some latitude in interpretation. Macroscopic Features Used for Classifying and 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 taste of the flesh are sometimes defining characters. 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. Size of the fruitbodies can vary within a species and so exact measurements are not always useful. However, “small,” “medium,” and “large,” based on the diameter of the mature caps, are handy Fig. 2. Tricholoma subresplendens, one of the white-capped tricholomas. It descriptors. Typically, “small” refers to is a W.A. Murrill species that is very similar to, or perhaps the same as, T. caps with diameter usually less than 5 columbetta. Photo by Bill Roody. cm; “medium” to caps usually between “gutter” around the stalk formed by the Although gill attachment is rarely, 5 and 10 cm, and “large” to caps usually emarginate gills. Because the concept if ever, used to help differentiate greater than 10 cm. now is based in part on microscopic species within Tricholoma, it is an The stalk is usually more or less features (mostly their absence), important character for recognizing the equal but may be swollen in the middle sometimes it is necessary to use a genus. Usually it is described as being (ventricose), tapered downward, or microscope to be certain that you emarginate, notched, or sinuate (Fig. 1). enlarged to slightly bulbous at the have a tricholoma. Unfortunately, gill attachment can be a base. It is fleshy or fibrous like the cap rather variable feature and these terms and can be solid, stuffed, or hollow. Its have been interpreted differently from surface usually is dry and longitudinally mycologist to mycologist (Leonard, striate, but also can be nearly smooth, In paperback 2000). C.H. Kauffman (1918) described appressed-fibrillose, scaly, or slightly February 1, 2013 the variability nearly a century ago. scurfy (at the apex only). Stalk color “Theoretically, they (the gills) are always often is white, but it may be tinged emarginate behind, but this condition with the cap color, or, more rarely, fully varies considerably. It is true that, in the concolorous with the cap. mature plant, when the pileus is fully A number of tricholomas have a expanded, they become either sinuate cortina. In these species, the veil usually or emarginate in most cases, although is delicate and may be visible only on a single specimen may not always be very young specimens, leaving just a normal in this respect. When young, trace of fibrils as a faint ring-zone on the however, they often do not show this upper portion of the stalk or a fringed character clearly, but are then adnexed, margin on the cap. A few species have a rounded-adnate, or adnate in such a way more substantial membranous veil that that they are merely a little less broad leaves a more or less prominent ring on at the attached portion than they are the stalk. a few millimeters from the stem, and Staining of the cap surface or, this short distance is often marked by more commonly, the gills and a straight edge rather than a rounded stalk, from bruising, handling, or edge... In old stages the gills may even with age is sometimes important become spuriously decurrent.” Thus, in distinguishing between species. when attempting to determine the gill Color-change reactions following attachment of a putative tricholoma, it the application of chemicals to the is best to examine multiple specimens fruitbody (“macrochemical” reactions) are not used widely in identifying 24 FUNGI • Volume 5:5 • Winter 2012 Fig. 4. Tricholoma floridanum, another of the yellow- capped tricholomas. This is one of the many not-well- Fig. 3. Tricholoma arvernense, one of the yellow-capped known species described by W.A. Murrill from Florida. tricholomas. It was added to the North American list Photo by Alan and Arleen Bessette. only recently when a DNA sequence from a collection Morphologically Similar Genera made in Idaho by Andrew Parker was found to be Following Fries’s initial definition of Tricholoma, some nearly identical to that of European material. It also has of the species he included in the genus were transferred to been found in California, Oregon, Washington, Alaska, other existing or newly created genera, such as Calocybe, and possibly Newfoundland. Photo by Sava Krstic. Dermoloma, Lepista/Rhodopaxillus, Leucopaxillus, Lyophyllum, Melanoleuca, Porpoloma, Rhodocybe, Tephrocybe, Tricholomopsis, and Tricholosporum. Because many of the tricholomas, but can be important in some cases. Potassium mushrooms in these pale-spored genera share the essential hydroxide (KOH), ammonium hydroxide (NH4OH), and macroscopic features of tricholoma, they can be mistaken for a paradimethylaminobenzaldehyde (PDAB) are of most use.