Trial field key to the species of TRICHOLOMOPSIS in the Pacific Northwest

Prepared for the Pacific Northwest Key Council
By Elsie Coulter, North Idaho Mycological Association

Reformatted by Lynda Foreman and Ian Gibson 2003
Name update by Ian Gibson 2017

Copyright © 1975, 2003, 2017 Pacific Northwest Key Council

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Do not copy photos without permission

INTRODUCTION

The following key contains all species of the Tricholomopsis genus found and reported in the Pacific Northwest region to date. The key does not represent original research but is material gathered from "Tricholomopsis (Agaricales) In The Western Hemisphere" (Brittonia 12:41-70, January 1960) by Alexander H. Smith, and Mushrooms Of North America by Orson K. Miller, Jr.

This key was designed to be followed mainly by field characteristics for the benefit of those without a microscope.

A simplified description of the genus as defined by Singer (1939) is as follows:

The spore deposit is white. The gills are variously attached to the stalk but never free from the beginning: stalk and cap are confluent. No veil is typically present but if so it is rudimentary and scarcely leaves a zone on the stalk. The stalk is subcartilaginous to fleshy. Most species live on the wood of conifers. (Spores smooth, thin-walled, yellowish in Melzer’s solution; pleurocystidia present and characteristic in most species, cheilocystidia regularly present but variable both as to size and shape; gill trama typically subparallel, of hyaline thin-walled hyphae; clamp connections regularly present.)

Color is perhaps the most important distinguishing characteristic for species in the genus. In some species actually living on wood, the mycelium may grow out and away from its original starting point and the fruiting body will appear to be growing on the ground. Such may be the case for T. resinosa but only laboratory studies on the nutrition of the species could tell us for sure.

Many of these species were formerly placed in other white-spored genera such as Collybia, Tricholoma, Pleurotus, Melanoleuca, and Clitocybe.

Name update (2017). In the original key both Megacollybia fallax and Megacollybia platyphylla were in Tricholomopsis. This key follows Smith’s key in differentiating them by the yellowish stem flesh (at least in cortex), although other features are noted in the text. Hughes et al.(2008) studied the Megacollybia platyphylla group including both species. They found that western North American collections from Washington, Idaho, Alaska, and Arizona corresponded in DNA sequencing to the Idaho type of Tricholomopsis fallax. The differentiation by the color of the flesh of the stalk is therefore suspect for leads 2a and 2b, as the true Megacollybia platyphylla has not been documented outside Eurasia – Megacollybia fallax can still be differentiated from Tricholomopsis radicata by the root-like extension of the stem of the latter without changing the rest of the key.

KEY TO SPECIES

1a Ground color of cap essentially gray

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1b Ground color of cap essentially yellow or olivaceous

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2a Flesh of stalk cortex yellowish, pith paler

................................................................................Megacollybia fallax

CAP 4-7(12) cm broad, 3-5 cm high, obtuse when young, margin incurved, remaining unexpanded or becoming broadly convex to nearly plane; surface dry and more or less streaked with gray fibrils, soon cracking around edge exposing white context; odor and taste not distinctive. GILLS pallid in button stages but becoming pale yellow, adnate, close, broad, not changing color when bruised. STEM 8-11cm long, 1.0-1.7 cm thick, equal or nearly so, solid, surface white to pale yellow but paler than gills, naked except for fibrillose striations. MICROSTRUCTURES spores 6-7.5 x 5-6 u (Smith), (5.6)6–8.5(10) x (4.0)5–7(8.0) um (Hughes et al.). NOTE It is likely that the stalk flesh can be whitish in this species, as Smith identified collections as M. platyphylla from Oregon and Washington.

2b Flesh of stalk white to grayish-white

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3a Stalk radicating (with root-like extension)

................................................................................Tricholomopsis radicata

CAP 5-7.5 cm broad, fleshy, firm, convex, dry, minutely silky fibrillose, somewhat shining, pale grayish brown, the center usually darker and often tinged with reddish brown, margin thin, cuticle separable; flesh white. TASTE disagreeable. GILLS thin, close, depressed at apex of stalk, adnexed, having a decurrent tooth, white. STEM 1.5-4 cm long, firm, nearly equal, hollow, with a small cavity, slightly fibrillose, white. MICROSTRUCTURES spores 6-7 x 3.5-5 u. REMARKS Occurrence in Pacific Northwest is uncertain.

3b Stalk not radicating

................................................................................Megacollybia platyphylla group

(It was known as Tricholomopsis platyphylla, Collybia platyphylla, and Oudemansiella platyphylla), but these names are probably misapplied in N. America (Hughes et al.). There are North American spp. in this group besides M. fallax but they have not been documented for our area. If stem is not radicating, see M. fallax 2a.

CAP 3-20 cm broad, convex, flat or slightly depressed in age, dry to moist, without fibrils or with scattered fibrils, from blackish brown to whitish gray, with short faint striations when wet. GILLS distant, very broad, veined, white to gray. STEM 6-12 cm long, 1-3 cm thick, equal or enlarging toward base, smooth, without fibrils, or with flat-lying fibrils, dry or moist, white to grayish white, hollow in age. VEIL absent. MICROSTRUCTURES spores 7-9(10) x 4.5-6 um (Smith), 6-10 x 5-7 for group (Hansen et al.).

Megacollybia platyphylla group Andrew Parker

4a (1b) Cap fibrillose

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4b Cap glabrous

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5a Cap context pallid yellow

................................................................................Tricholomopsis thompsoniana

CAP 2.5-6 cm broad, broadly convex to nearly plane, surface glabrous, moist, yellow variegated with pallid areas, staining darker yellow where handled or bruised. ODOR not distinctive. TASTE mild. GILLS broad, subdistant, adnexed, faces yellowish, edges pallid but staining yellow where bruised. STEM 4-7 cm long, 0.4-1.1 cm thick, equal, solid, pallid, staining darker, glabrous. MICROSTRUCTURES spores 5-8 x 5.5-6.5 u. REMARKS This species was for a while called T. flavescens.

Tricholomopsis thompsoniana Kit Scates Barnhart

5b Cap context grayish-olivaceous

................................................................................Tricholomopsis glaucipes

CAP 3-7 cm broad, obtusely umbonate, margin spreading, opaque, surface unpolished from a powdery covering but appearing moist at first; ground color yellowish, more or less streaked; flesh watery, thick in the umbo, thin over the gills. ODOR slightly fragrant. TASTE mild. GILLS depressed-adnate, or with slight tooth, broad and somewhat ventricose, intervenose, yellow. STEM 6-8 cm long, 0.9-1.2 cm thick at apex, base enlarged somewhat, interior soon grub-eaten and brownish, surface hoary and unpolished, pallid with reflection of yellowish until hoary coating rubbed off, then changing to sordid brown. MICROSTRUCTURES spores 6.5 x 4-5.5 u.

6a (4a) Cap with purple-red or brick-red squamules or fibrils

................................................................................Tricholomopsis rutilans

CAP 3-8 cm broad, obtuse with incurved often ribbed margin, expanding to campanulate and finally nearly plane, usually retaining a low obtuse umbo; surface dry and tomentose-squamulose, and more granular-roughened than scaly; strong yellow cast finally showing beneath the fibrillose layer, or often yellowish where bruised; flesh thick, pale yellow. ODOR none. TASTE slight or radish. GILLS adnate becoming adnexed, narrow, crowded, yellow, edges crenulate. STEM 5-10 cm long, 0.8-1.5 cm thick at apex, up to 2.5 cm at slightly enlarged base, stuffed becoming hollow, yellowish within; surface covered with appressed reddish fibrils with a paler zone at apex, staining yellow where handled. MICROSTRUCTURES spores 5-6 x 3.5-4.5 u.

Tricholomopsis rutilans Steve Trudell

6b Caps with gray, yellow, light to dark brown fibrils or squamules

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7a Veil present, at least when young

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7b Veil absent

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8a Stem not staining when handled

................................................................................Tricholomopsis decora

CAP 4-6 cm broad, convex with an incurved tomentose margin; surface appearing moist beneath gray to brownish gray fibrillose scales, ground color some shade of yellow and fading to paler yellow; flesh yellow, thin to moderately thick, watery. ODOR not distinctive. TASTE mild. GILLS adnexed or with a decurrent tooth, bright yellow or finally tinged orange. STEM 4-6cm long, 0.5-1.0 cm thick, equal or nearly so. MICROSTRUCTURES spores 6-7.5 x 4.5-5u. REMARKS The striking field characteristic of this species is the overall yellow coloration with small grayish squamules.

Tricholomopsis decora Steve Trudell

8b Stem staining when handled

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9a Growing on ground; cap with distinct resinous feel

................................................................................Tricholomopsis resinosa

CAP 3-7 cm broad, convex to obtuse, margin incurved, expanding to nearly plane, surface with resinous feel (but not viscid from a gelatinous pellicle); ground color yellow but obscured by brown fibrillose squamules, becoming russet on drying; flesh yellowish. ODOR and TASTE not recorded. GILLS adnexed, broad, close, pale yellow with darker yellow edges. STEM 4-7 cm long, 1 cm thick, equal or enlarged at base; color like cap, covered with squamules which discolor to russet when handled or on drying, with distinct resinous feel. MICROSTRUCTURES spores 5-6 x 4.5-5 u. REMARKS Rare, collected once in Mt. Rainier National Park.

9b Growing on wood; cap lacking resinous feel

................................................................................Tricholomopsis bella

CAP 6.5 cm broad, depressed around low umbo; margin decurved, surface coarsely fibrillose, slightly squamulose on the umbo and near the margin; color evenly dull yellow, flesh same as cap. ODOR and TASTE not distinctive. GILLS adnexed, close, broad, dull yellow, staining dull rusty brown when bruised. STEM 2 cm long, 0.9 cm thick, nearly equal, hollow, firm, pallid yellowish within, the surface cap color and fibrillose near the base with dull yellow fibrils, slowly staining brown where handled at least on the fibrils. MICROSTRUCTURES spores 6-7 x 5-5.5 u.

Tricholomopsis bella Kit Scates Barnhart

10a (7a) Stalk staining on handling

................................................................................Tricholomopsis fulvescens

CAP 3-5 cm broad, with inrolled margin, surface dry and appressed-fibrillose, ground color yellow; flesh yellowish. ODOR and TASTE not distinctive. GILLS pale yellow, near cinnamon brown when dried, only moderately close, broad, depressed-adnate. STEM 6-9 cm long, 1 cm thick at apex, narrowly clavate, hollow, watery yellow within and darkening where cut; surface appressed-fibrillose with yellow veil elements which become rusty brown when handled; apex silky and paler. Mycelium around the base yellow. MICROSTRUCTURES spores 8-10 x 6-7 u.

10b Stalk not staining on handling

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11a Taste and odor not distinctive

................................................................................Tricholomopsis sulfureoides

CAP 3-7 cm broad, broadly convex, rounded when young, margin inrolled, becoming expanded and plane to slightly depressed, sometimes retaining a slight umbo; surface pale yellow, or variegated with paler areas, slightly fibrillose becoming squamulose and darkening to brownish in age; flesh thin, equal, pale yellow like cap surface and unchanging when cut or bruised. STEM 3-6 cm long, 0.7-2 cm thick, central to eccentric, equal or enlarged downward; yellow but paler than the gills above and darker below, fibrillose on the lower part from remains of a thin veil, naked in age. MICROSTRUCTURES spores 5.5-5-6 x 4.5-5 u.

Tricholomopsis sulphureoides Kit Scates Barnhart

11b Taste slightly peppery; odor faintly fragrant

................................................................................Tricholomopsis flavissima

CAP 3-5 cm broad, convex, becoming broadly convex, surface dry and fibrillose, somewhat scaly around disc; color evenly yellow overall or disc darker; flesh thin but nearly equal, dull yellow. GILLS close to subdistant, bluntly adnate but becoming more or less decurrent, light yellow and becoming light orange yellow, the edges a brighter yellow than the faces (appearing gelatinous under a lens). STEM 2-5 cm long, 0.3-0.6 cm thick, equal, hollow, fleshy, concolorous with the cap in age, pallid when young from the thin pale yellowish partial veil, in age appressed-fibrillose to the apex. MICROSTRUCTURES spores globose, 7-9 u.

Tricholomopsis flavissima Buck McAdoo

REFERENCES

1. Hughes, Karen W. et al. (2008) [2007]. “Megacollybia (Agaricales)”. Rep. Tottori Mycol. Inst. 45: 1-57.
2. Miller Jr, Orson K. 1972. Mushrooms of North America. E.P. Dutton. New York. Chanticleer Press.
3. Miller Jr., Orson K., Hope H. Miller. 2006. North American Mushrooms. A field guide to edible and inedible fungi. Falcon Guide. (more recent version of above). 
4. Smith, Alexander H. 1960. Tricholomopsis (Agaricales) in the Western Hemisphere. Brittonia 12: 41-70.

INDEX

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