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Tricholoma species 02: pessundatum, ustale

[ Basidiomycota > Agaricales > Tricholomataceae > Tricholoma . . . ]

by Michael Kuo

This Tricholoma species is found in association with oaks in central Illinois, in late summer and fall. It is a member of the Tricholoma pessundatum species group—a group of species with sticky brown caps and whitish gills that develop reddish brown spots and stains. However, Tricholoma pessundatum is a European species associated with conifers. Tricholoma ustale is another similar, well-known European species—but it is associated with European beeches. Several less well-known species from southern Europe have been described in association with oaks, but it is unlikely that these would have transcontinental distribution. In short, in North America we likely have a number of pessundatum-like, undescribed species in need of substantial taxonomic energy and focus.


Ecology: Mycorrhizal with oaks; growing scattered or gregariously; late summer and fall; distribution uncertain. The illustrated and described collections are from central Illinois.

Cap: 3.5–8 cm; convex with an inrolled margin when young, becoming broadly convex when mature; sticky when fresh but soon dry; bald; soft; orangish brown to reddish brown, fading to orangish tan; the center usually darker than the margin; the margin not becoming lined.

Gills: Attached to the stem by a notch; close; short-gills frequent; white to beige; discoloring and spotting rusty brown with age, especially on the gill edges; eventually becoming cinnamon colored overall.

Stem: 4–7 cm long; 1–2 cm thick; more or less equal; bald or finely silky; whitish when young, becoming brownish to reddish brown; basal mycelium white.

Flesh: White; unchanging when sliced.

Odor and Taste: Strongly mealy.

Chemical Reactions: KOH reddish brown on cap surface.

Spore Print: White.

Microscopic Features: Spores 6–7.5 x 3.5–5 µm; ellipsoid; apiculate; smooth; inamyloid; hyaline in KOH. Basidia 4-sterigmate. Pleurocystidia not found. Cheilocystidia not found. Pileipellis an ixocutis of cylindric elements 3–7.5 µm wide, smooth or finely encrusted, reddish brown en masse in KOH. Clamp connections not found.

REFERENCES: (Bessette et al., 2013; Christensen & Heilmann-Clausen, 2013.) Herb. Kuo: 09260803, 09290802, 10251706.

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Tricholoma species 02

Tricholoma species 02

Tricholoma species 02

Tricholoma species 02

Tricholoma species 02

Tricholoma species 02

Tricholoma species 02
Spore print

Tricholoma species 02

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Kuo, M. (2019, September). Tricholoma species 02: pessundatum, ustale. Retrieved from the MushroomExpert.Com Web site: