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Tricholoma populinum

by Michael Kuo, 23 April 2025

This primarily northern and montane Tricholoma can be recognized by its mycorrhizal association with poplars (trees in the genus Populus), its orangish brown cap, its mealy odor, and the reddish brown spotting that develops on the gills as the mushroom matures. In North America it is often found in association with narowleaf cottonwood or balsam poplar.

The "true" Tricholoma populinum is European and, depending on how you want to break things up, it may not occur in North America. One western North American version has been given a name (unfortunately, without peer review and without molecular support, in an irresponsible online publication); it may or may not correspond to the collection described here, which is from British Columbia. However, it is possible that if small ITS differences are to be the standard for species in the populinum group, more "new species" await.

Thanks to Regan Dixon for collecting, documenting, and preserving Tricholoma populinum for study; her collection is deposited in The Herbarium of Michael Kuo.

Description:

Ecology: Mycorrhizal with poplars, including narowleaf cottonwood, quaking aspen, and balsam poplar; growing gregariously; originally described from Sweden (Fries 1869); and neotypified from Denmark (Christensen & Noordeloos 1999); fairly widespread in Europe and North America, primarily in northern and montane areas; summer and fall. The illustrated and described collection is from British Columbia.

Cap: 3–10 cm; convex becoming broadly convex and eventually plane; sticky when fresh but soon dry; bald; orangish brown overall, but sometimes paler at the margin; the margin at first inrolled, but straightening out with development, and not becoming lined.

Gills: Attached to the stem by means of a notch; close; short-gills frequent; whitish, becoming dirty cream colored and developing reddish brown spots and discolorations.

Stem: 3–6 cm long; 1–2 cm thick; more or less equal above a slightly enlarged base; bald; dry; white at the apex; becoming brownish below; staining and discoloring reddish brown; basal mycelium white.

Flesh: White; firm; not changing on exposure.

Odor: Mealy.

Chemical Reactions: KOH red on dried cap surface and on rehydrated cap surface; probably red on fresh material as well.

Spore Print: White.

Microscopic Features: Spores 4–5 x 2–3 µm; ellipsoid, with a tiny apiculus; smooth; hyaline in KOH, inamyloid. Basidia 26–30 x 3–5 µm; subclavate; 4-sterigmate. Cystidia not found. Pileipellis an ixocutis; elements 2–5 µm wide, smooth or (infrequently) a little encrusted, hyaline to brownish in KOH. Clamp connections not found.

REFERENCES: J. E. Lange, 1933. (Ovrebo, 1973; Smith, 1975; Smith, Smith & Weber, 1979; Ovrebo, 1980; Arora, 1986; Riva, 1988; Breitenbach & Kränzlin, 1991; Schalkwijk-Barendsen, 1991; Lincoff, 1992; Shanks, 1994; Noordeloos & Christensen, 1999; Nonis, 2007; Boccardo et al., 2008; Buczacki et al., 2012; Grubisha et al., 2012; Bessette et al., 2013; Christensen & Heilmann-Clausen, 2013; Evenson, 2015; Cripps, Evenson & Kuo, 2016; Christensen & Heilmann-Clausen, 2018; Læssøe & Petersen, 2019; Kibby, 2020; Trudell & Parker, 2021; Landry et al., 2022; Ding et al., 2023.) Herb. Kuo 10092401.

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Spore print

Spores

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Cite this page as:

Kuo, M. (2025, April). Tricholoma populinum. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/tricholoma_populinum.html