Tylopilus rubrobrunneus

Description
Mushroom Identification

Description

Tylopilus rubrobrunneus is a bolete fungus in the family Boletaceae. This beautiful, bitter-tasting eastern North American mushroom is very common in some years—and seemingly absent in others. In my area (central Illinois), at least four species of Tylopilus can look very similar, especially at maturity, when their caps have faded to tan.

It is too bitter to eat but useful for unique approaches like cocktail bitters. It isn’t toxic; just absurdly bitter.

T. rubrobrunneus was first described scientifically in 1967 by Samuel J. Mazzer and Alexander H. Smith from collections made in Michigan. It is found in the United States; the bolete was reported from a Mexican beech (Fagus mexicana) forest in Hidalgo, Mexico in 2010.

Common names: Reddish Brown Bitter Bolete.

Mushroom Identification

Ecology
Mycorrhizal with oaks and other hardwoods; growing alone, scattered, or gregariously; summer and fall; widely distributed in North America east of the Rocky Mountains.
Cap
5–15 cm; convex, becoming broadly convex or nearly flat in age; dry; finely felty when young, becoming bald and soft-leathery; brownish-purple to purplish brown when young, becoming purplish brown, brown, or fading to tan; the young margin whitish and incurved.
Pore Surface
Whitish, becoming pinkish and finally dingy brown; bruising pinkish to brownish; pores circular, 2–3 per mm; tubes to 10 mm deep.
Stem
7–14 cm long; 1.5–4 cm thick; more or less equal, or club-shaped; whitish to brownish or brown; typically developing olive to olive-brown stains or bruising olive; bald; sometimes very finely reticulate near the apex; basal mycelium white.
Flesh
Thick and white; unchanging when sliced; soft; often discolored olive around wormholes.
Odor and Taste
Taste very bitter; odor is not distinctive.
Chemical Reactions
Ammonia negative on cap surface; negative on flesh. KOH rusty orange on cap surface; negative on flesh. Iron salts negative on cap surface; negative to pinkish on flesh.
Spore Print
Dull pinkish to reddish-brown.
Microscopic Features
Spores 9–14 x 2.5–4 µm; fusiform; smooth; faintly ochraceous in KOH. Hymenial cystidia inconspicuous; not or only slightly projecting; fusoid-ventricose; hyaline in KOH. Pileipellis is a collapsing trichoderm; golden to hyaline or brownish in KOH; elements 2.5–7.5 µm wide, smooth; terminal cells ranging from cylindric with rounded apices to fusiform-cystidioid.