Summary:
Gymnopus acervatus is recognized by its hygrophanous reddish brown cap, its reddish brown stem with fine hairs over lower part, bundled growth habit on wood, and white spore deposit. In old fruiting bodies, the buff cap contrasts with the red-brown stem, but when young the cap and stem are similar in color. Hughes(4) have proposed a new genus Connopus R.H. Petersen to accommodate this species, and the online Species Fungorum, accessed January 17, 2015, gave the current name as Connopus acervatus (Fr.) K.W. Hughes, D.A. Mather & R.H. Petersen, Mycologia 102(6): 1467 (2010), but MycoBank, accessed the same date, gave the current name as Gymnopus acervatus. Hughes(4) also point out differences between western North American and eastern North American populations that might eventually require a separate species designation. Gymnopus acervatus is common in the Pacific Northwest in summer and fall (Arora).

Cap:
(0.7)1.5-4.5cm across, convex with incurved to inrolled margin, expanding to flat or sometimes slightly depressed when old; hygrophanous, reddish brown when young, fading with age or drying to brownish on the disc and buff along the margin, eventually buff nearly overall; dry to moist, bald, margin usually opaque but sometimes translucent-striate, (Halling), 1-4(5)cm across, convex with incurved margin, becoming broadly convex when old; hygrophanous, dark reddish brown fading to pale reddish brown, pinkish buff or paler "sometimes with darker and lighter zones" as it dries; smooth, not viscid, (Arora), young unexpanded clusters often have a characteristic reddish purple color, (Trudell)

Flesh:
thin; whitish, (Halling), thin; pallid, (Arora)

Gills:
adnexed to adnate, close to crowded, narrow, thin; whitish, developing pale pinkish tones when old; edges even, (Halling), "typically adnexed or notched or free", close or crowded, narrow; white to dingy pinkish or vinaceous buff, (Arora)

Stem:
(1.5)3-7(8)cm x 0.15-0.3(0.6)cm, "equal, fibrous but somewhat brittle", hollow, bases usually confluent; reddish brown to brown in upper part, sometimes with a violet tint, "strigose to pubescent with a whitish vesture toward the base"; dry, shiny bald, (Halling), 4-12cm x 0.2-0.6cm, more or less equal, "hollow, pliant but brittle"; reddish brown to vinaceous brown or sometimes paler when old; dry, smooth in upper part, "with fine whitish hairs over lower half or at base", (Arora)

Odor:
not distinctive (Halling)

Taste:
not distinctive, (Halling), faint, slightly bitter, (Buczacki)

Microscopic spores:
spores 5-7 x 2-3 microns, elliptic, smooth, inamyloid, (Arora), spores 5.6-6.4(7) x 2.5-3 microns, cylindric to ellipsoid in face view, lacrymoid [tear-shaped] to elliptic or slightly subreniform [kidney-shaped] in side view, smooth, inamyloid, acyanophilic; basidia 4-spored, 24.5-35 x 5.6-6.4 microns, clavate, not siderophilic; pleurocystidia absent, cheilocystidia inconspicuous, scattered, buried somewhat on gill edge, 24.5-42 microns long, "fusoid, irregularly clavate, less often variously lobed to diverticulate"; clamp connections present in all tissues, (Halling)

Spore deposit:
white to pale cream (Halling), white (Arora, Miller)

Notes:
There are collections from BC at the Pacific Forestry Center and the University of British Columbia. The University of Washington has collections from WA, ID, AK, and NM. Oregon State University has material from OR. It occurs in CA according to MykoWeb. It also occurs more widely in North America, in Europe, and in Mexico.

EDIBILITY

not edible: said to bitter when cooked and slightly poisonous to some, (Arora)

Synonyms and Alternate Names:
Collybia acervata (Fr.) P. Kumm.
Marasmius acervatus (Fr.) Pearson & Dennis