Summary:
Section Calodontes (Smith), Section Rubromarginatae (Maas Geesteranus). Mycena rubromarginata is characterized by small size, gray (or occasionally white) colors with dull reddish-brown gill edges, its habitat, large spores, and fusoid-ventricose cheilocystidia. The description is derived from Smith(1) except where noted,. The Courtecuisse description is for M. rubromarginata (Fr.: Fr.) Kummer.

Cap:
0.7-2cm across, obtusely conic to convex becoming bell-shaped to broadly convex; "dark gray with a vinaceous tinge, soon becoming paler gray, the disc remaining darker than the margin, sometimes the margin tinged reddish at first"; moist, densely pruinose in buttons but soon naked, (Smith), up to 3cm across, grayish beige with pinkish or pinkish brown tints; pruinose, striate, (Courtecuisse)

Flesh:
thin, fragile, watery; grayish to pallid

Gills:
ascending, broadly adnate with slight tooth, subdistant, 12-17 reaching stem, 1 or 2 tiers of subgills, gills moderately broad (about 0.3cm), interveined; pallid to dull grayish with bright reddish brown edges that soon become sordid reddish brown (as seen under a hand lens)

Stem:
2-4(7)cm x 0.1-0.35cm, equal, fragile, hollow, round in cross-section or compressed; pale watery gray, translucent; bald, base bald or nearly so, (Smith), gray brown then pale pinkish brown; fibrillose in lower part, (Courtecuisse)

Veil:
[none]

Odor:
not distinctive

Taste:
not distinctive

Microscopic spores:
spores 10-12 x 5-7 microns, broadly elliptic, smooth, germinating readily (germinated spores often found in spore deposit), amyloid; basidia 4-spored; pleurocystidia rare, cheilocystidia 28-42 x 8-12 microns, broadly fusoid-ventricose when young, elongating and when old somewhat irregular or narrower, tops sometimes forked

Spore deposit:
almost white (Breitenbach)

Notes:
Mycena rubromarginata has been found at least in BC and OR, is not uncommon from NY to OR, and extends south in the mountains to NC and TN. (Smith(1)). There are collections from WA, AK, and MI at the University of Washington. It occurs in Iceland and Europe (including the type locality in Sweden), (Maas Geesteranus). Breitenbach(3) give the distribution as North America, Europe (including Switzerland), and North Africa.

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