Summary:
Distinctive field characteristics of Marasmiellus peronatus are yellow gills when young and acrid [peppery] taste according to Halling(2). Other features include a reddish brown to buff cap +/- a yellow tint, a stem colored about as the cap or yellowish (the stem base often covered with yellow hairs), and abundant whitish or yellowish mycelium permeating the substrate. |Gymnopus peronatus was moved in 2019 to Marasmiellus but there are problems with the placement and it is likely not to be permanent. |Gymnopus subnudus has been frequently misidentified as this taxon in the past according to Halling and he uses the acrid taste of M. peronatus as one of the characters to differentiate it from G. subnudus with bitter or sometimes absent taste.

Gills:
the same color as cap or lighter, (Moser), cream to yellow brown, (Hansen), free, distant, narrow; brownish or yellow ocher, (Courtecuisse), distant, broad; yellow when young, (Halling), free, 60-70 reach stem, 3-7 subgills between pairs of gills; light brownish to yellow, also with a lilac tint; edges with pale flocci, (Breitenbach)

Stem:
3-7cm x 0.3-0.5cm, colored as gills, (Moser), 3-7cm x 0.3-0.5cm, colored as cap; strigose in lower half, (Hansen), up to 8cm long and up to 0.5cm wide, concolorous or yellow; "pruinose to shaggy with bright yellow hairs below", (Courtecuisse), 5-8 x 0.3-0.5cm, cylindric, widened somewhat at base; base covered with yellowish mycelium, with yellow-brownish longitudinal fibrils above, "smooth to somewhat longitudinally grooved, sometimes also tomentose to strigose", (Breitenbach), tough; yellowish to yellowish brown, darker when old; longitudinally fibrillose, the enlarged base "covered with hairs and strands connected to an abundant whitish to yellowish mycelium that permeates the leaf litter", (Trudell), horny in consistency (Brian Luther, who has seen robust fruitbodies up to 35cm tall, pers. comm.)

Veil:
[presumably none]

Odor:
none (Moser), of vinegar when rubbed (Courtecuisse), pleasantly spicy (Breitenbach), often pleasantly spicy (Trudell)

Taste:
acrid (peppery), (Halling), +/- burning sharp (Moser), at first mild, then pepper-hot, (Breitenbach, Trudell), bitter (but see NOTES above) (Hansen)

Microscopic spores:
spores 6-8 x 3-4 microns, (Moser), spores 6-9 x 3-4 microns, elliptic, (Hansen), 7.5-11.2 x 3.6-4.5 microns, elliptic to fusiform-elliptic, smooth; basidia 4-spored, 28-40 x 4.5-6 microns, cylindric-clavate, with basal clamp connection; cheilocystidia abundant, 70-100 x 4-7 microns, "slenderly fusiform, most rostrate to branched apically", pleurocystidia similar but less abundant, (Breitenbach(3) who note however discrepancy in spore sizes from other descriptions, and also note Lange''s comment that some authors consider Marasmius peronatus to be a large-spored form and M. urens a small-spored form)

Spore deposit:
light cream-ocher (Breitenbach)

Notes:
M. peronatus is known from WA, OR, and Europe (Halling), and it is reported from Mexico (Guzman(2)), North Africa and Asia (Breitenbach). Collections from BC are deposited at the University of British Columbia.

EDIBILITY

Synonyms and Alternate Names:
Gymnopus peronatus "(Bolton: Fr.) Antonin, Halling, & Noordel. "