Summary:
Callistosporium luteo-olivaceum has the stature of a Collybia (in the older sense that included Gymnopus and Rhodocollybia) and was originally in that genus. It is distinguished by an olive and yellow coloration and a tendency to grow on rotten wood. Redhead(23) provides a taxonomic review of this species. The description is derived from Arora except where noted. This taxon may represent more than one species. MycoBank, accessed October 21, 2018, placed Callistosporium in Catathelasmataceae, but the online Index Fungorum, accessed the same day, had it in Tricholomataceae (as well as keeping Catathelasma in Tricholomataceae but having Pseudolaccaria in Catathelasmataceae).

Cap:
1.5-6.5cm across, convex or slightly umbonate becoming flat or shallowly depressed; dark olive to olive brown or olive yellow, often becoming yellower (yellow-brown to honey-colored) when old and developing dark reddish brown tones when dried; "not viscid, often minutely scurfy at first but becoming smooth", (Arora), yellow-brown to liver-brown, (Trudell)

Flesh:
thin; pallid or yellow or tinged cap color, (Arora)

Gills:
notched or adnexed or adnate, close; yellow to golden yellow, tending to redden when dried, (Arora), close, thin; yellow to ocher or olive-tinted, (Trudell)

Stem:
2.5-7cm x 0.3-1cm, "equal or slightly thicker at either end, often flattened"; colored like cap or slightly darker, tending to turn deep reddish brown from the base up as it dries; smooth to fibrillose or scurfy especially over lower part, sometimes streaked when old, (Arora), hollow; similar in color to cap, with yellow tomentum at base; fibrillose, (Trudell)

Odor:
mild to pungent or slightly fruity, (Arora)

Taste:
mild or slightly bitter, (Arora), both North American and European collections often reported as slightly bitter or styptic, (Redhead), farinaceous-bitter (Trudell)

Microscopic spores:
spores 4.5-6.5 x 3-4.5 microns, elliptic to nearly round, with hilar appendage, smooth, not amyloid but many of them stain wine-colored in KOH, (Arora), spore size varies up to at least the dimensions of the type of C. graminicolor Lennox measured by Redhead as 6.2-7 x 4-4.5 microns, and Redhead relates that Favre measured spores sizes for 4-, 2-, and 1-spored basidia as (respectively) 7-8(8.5) x 3.5 microns, 9-11 x 3.8 microns, and 12-15 x 4.5-4.8 microns, (Redhead), basidia 4-spored, noncarminophilous, 22-30 x 6-7.5 microns; pleurocystidia absent, cheilocystidia generally present, inconspicuous, rarely exceeding basidia, 10-39 x 2.5-5 microns, colorless, clavate to filamentous, usually with contorted appearance, sometimes sparingly branched, (Lennox)

Spore deposit:
white (Arora)

Notes:
Collections were examined from BC, WA, ON, QC, FL, ME, NC, NY, TN, VA, Venezuela, Italy, and Switzerland, and it is also known from northern Africa, (Redhead). It was reported by Jake Hurlbert from OR.

EDIBILITY

unknown (Arora)

Synonyms and Alternate Names:
Callistosporium luteofuscum Singer