Summary:
Gymnopus fuscopurpureus is recognized by reddish-brown to dark brown color, a convex to flat cap, a finely hairy stem, dense gregarious or clustered growth on ground or woody debris, a white spore deposit, a green reaction in KOH (alkali), and encrusting pigments that are not soluble in alkali. The description in Arora(1) is for Collybia fuscopurpurea group, which may include other species such as a species in California differing in its paler but more tawny colors and in the absence of an alkali reaction. For a further discussion of the presence of the alkali reaction, of the solubility of encrusting pigments, and of differences from Gymnopus alkalivirens, see SIMILAR sections of the two species.

Cap:
2-3.5cm across, convex to broadly convex, then flat-convex to flat-depressed with uplifted margin; hygrophanous, dark reddish brown overall, soon fading to reddish brown to light brown or brownish orange near margin, disc remaining dark reddish brown, at maturity often fading to grayish orange but with a darker disc; bald, shiny when moist, dull when dry, smooth to slightly subrugulose [somewhat finely wrinkled] near margin, (Halling), (0.5)1-3(4)cm across, convex to nearly flat or subumbilicate; hygrophanous, dark reddish brown to reddish straw or cinnamon, with irregular blackish stains; lubricous, smooth, margin translucent-striate, (Guzman)

Flesh:
soft, thin (up to 0.2cm thick), brownish orange; in stem brownish gray, (Halling), thin, subleathery [somewhat leathery]; whitish to reddish brown, (Guzman)

Gills:
"adnexed when young becoming broadly adnate, sometimes pulling free, close to subdistant, narrow to moderately broad but evenly spaced", 2-3 sets of subgills; brown when young and fresh, paler when old, usually with hoary sheen, (Halling), "subdecurrent to adnexed, subdistant", more or less thick and broad, sometimes interveined; colored as cap or light chocolate brown to blackish in dried state, (Guzman)

Stem:
up to 7.5cm long, up to 0.4cm wide, more or less round in cross-section at first, rarely cleft and compressed when old, equal or wider in lower part, stuffed, rarely subradicating [somewhat rooting], fibrous; minutely pruinose overall (with a hand lens), matted tomentose in lower part with a light brown tomentum, otherwise dark brown, black when old and when dried, (Halling), 4-7cm x 0.1-0.3(0.4)cm, uniform; colored as cap or vinaceous red, to nearly black when dried; fibrillose, slightly longitudinally grooved, smooth or slightly pruinose mainly at base, (Guzman)

Veil:
[presumably none]

Odor:
mild (Halling, Guzman)

Taste:
mild to slightly bitter (Halling), mild (Guzman)

Microscopic spores:
spores 6.7-8.5 x 3.3-4.8 microns, elliptic to lacrymoid [teardrop-shaped] to subfusoid [somewhat spindle-shaped] or rarely sublimoniform [somewhat lemon-shaped], smooth, inamyloid, thin-walled, colorless to greenish in alkali; basidia 4-spored, 28-38 x 6-7 microns, clavate; pleurocystidia absent, cheilocystidia 20-35 microns long, "subfusoid, cylindric or subclavate to clavate"; gill trama "descending, parallel, inamyloid, with scattered brown encrusting pigment becoming green in KOH", elements 3.5-7 microns wide; cap trama with hyphae 5-10 microns wide, "more or less interwoven but radially oriented, inamyloid, with scattered, brown, granular encrusting pigment becoming green in KOH"; cap surface "a layer of repent, branched hyphae, not diverticulate or coralloid, not radially arranged", "encrusted with a brown pigment that becomes green in alkali", elements 3-8 microns wide; stem surface a layer of parallel, vertically oriented hyphae with elements 3-7 microns wide, "encrusted with brown pigment, giving rise to long, tangled, branched, thin-walled caulocystidia, 3.5-7 microns wide, more abundant toward the base; clamp connections present; stem trama identical to gill trama; all tissues green with alkali, (Halling), spores (5)6.4-9(10) x 3-4.8(5) microns, lacrymoid or subelliptic, inamyloid, colorless or pale yellowish in KOH and in water; basidia 4-spored, 24-30.4 x 4.8-6.4 microns, clavate, colorless, frequently with clamp connections; pleurocystidia absent; cheilocystidia numerous, (14)18-45(60) x 4-6(8) microns, "cylindric, flexuous, irregularly lobulated, sometimes apically dichotomously or trichotomously lobulated", colorless, "yellowish or yellowish brown in water and greenish in KOH, frequently clamped at the base"; hymenial trama subregular, hyphae (3)4-10(16) microns wide, "yellowish to yellowish brown when observed in water, brown in mass, with very short and obscurely conspicuous granulations when observed in water; cap context with hyphae 3.2-4.8 microns wide, colorless or yellowish in water, "sometimes with short granulations observed in water"; cap cuticle not gelatinous, elements (3)5-8(10) microns wide, subspherical, "short and irregularly bifurcate, not radially arranged, punctate, incrustations brown when observed in water"; caulocystidia common, 22-65(90) x 3-5 microns, "cylindric, flexuous, sometimes irregularly lobulated, similar in color to cheilocystidia"; stem hyphae (3)5-15(18) microns wide, colorless to yellowish in water, "surface covered with very distinct strong granulations" (bigger than those of the hymenial and cap trama), brown when observed in water; "All granulations mentioned above, disappear in contact with KOH and hyphae appear smooth and stain greenish."; clamp connections common, (Guzman)

Spore deposit:
[presumably close to white]

Notes:
Halling(3) examined collections of Gymnopus fuscopurpureus from WA, AZ, CA, CO, Mexico, Belgium, and the Czech Republic, and reassigns collections from ID and OR to this species. Gymnopus fuscopurpureus has been reported from BC by O. Ceska and others and there are 24 collections at the University of British Columbia from BC.

EDIBILITY

unknown (Arora for Collybia fuscopurpurea group)

Synonyms and Alternate Names:
Collybia fuscopurpurea (Pers.: Fr.) P. Kumm.