Summary:
Distinctive characters are small stature and small elliptic to oval spores. Other features include a brown to orange-brown or red-brown, bald to minutely scurfy cap, adnate to notched, narrow, yellow gills that often discolor brown on the edges, a reddish brown stem that is scurfy to pruinose at the top, absent veil, bitter taste, growth on wood, and microscopic characters. It is a member of the Gymnopilus sapineus group but has no veil.

Cap:
1-2.5cm across, convex, obtuse; "Kaiser brown", deep tawny, bright-watery-cinnamon, orange-brown, rusty fulvous; bald to minutely scurfy, margin even, sometimes extending beyond cap margin, (Hesler), up to 2.5cm across, red-brown, rust brown, reddish yellow, also with ochraceous tone, (Moser), orange brown to dark orange-brown (Miller), orange-brown to yellow-brown; smooth, slightly striate edge, (Trudell)

Flesh:
thin on margin; tawny to ochraceous, (Hesler)

Gills:
adnate-seceding, sometimes emarginate with decurrent tooth, close to crowded, narrow; bright yellow then dull yellow, or rusty yellow, finally ferruginous and spotted, edges sometimes discoloring brown, (Hesler), rust-yellow, edges often discoloring brown, (Moser)

Stem:
1.5-3cm x 1.5-3cm (sic but probably means 0.15-0.3cm), "equal, solid or stuffed or hollow"; reddish brown or rusty bay, darker in lower part; top scurfy, sometimes throughout, (Hesler), 1-4cm x 0.1-0.3cm, reddish yellow to rust brownish; top pruinose, in lower part fibrous to bald, (Moser), red-brown with yellowish top and whitish longitudinal fibrils on lower part (Trudell)

Veil:
none, although an agaric reported from Europe under this name as showing a veil in the young stage, (Hesler)

Odor:
mild (Hesler)

Taste:
bitter (Hesler)

Microscopic spores:
spores 3.5-5.5 x 2.6-3.5 microns, elliptic to oval, verrucose [warty], often with a suprahilar depression, "no germ pore, ferruginous in KOH, dextrinoid"; basidia 4-spored, 17-22 x 4-5 microns, lactiferous basidioles "scattered to abundant on sides, with brownish amorphous contents", 16-19 x 4-5 microns; pleurocystidia 20-24 x 5-6 microns, "fusoid-ventricose with a filiform neck, capitate to subcapitate", cheilocystidia 14-26 x 3-5 microns, "flask-shaped, capitate or subcapitate"; gill trama parallel, hyphae 5-10 microns wide; cap trama radial, cap cuticle "of upright or subrepent hyphae, irregularly scattered or tufted, the terminal elements as pileocystidia", 28-35(50) x 5-15 microns, "clavate to saccate, more or less in a palisade or in tufts"; caulocystidia 20-37 x 5-10 microns, "brownish, clavate, spathulate, ellipsoid, at times subcapitate"; clamp connections present, (Hesler)

Spore deposit:
bright rusty yellow (Hesler)

Notes:
Material was examined from WA, OR, ID, CA, CO, CT, MA, ME, MI, NY, and TN, and the distribution was given as northern United States, Tennessee and Canada, (Hesler). There are collections from BC at the Pacific Forestry Centre in Victoria.

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