Cap 0.8-2.0 cm broad, convex, convex-umbillicate, to infundibuliform; margin decurved to level in age; surface radially appressed-fibrillose, the fibrils dark-brown over a pale-grey background, hygrophanous, fading in age to lighter shades of grey, sometimes with a satiny sheen when dry; context thin, approximately 1 mm thick, pale grey, unchanging; odor and taste not distinctive.
Gills subdistant, decurrent, medium-grey, up to 2 mm broad, the edges blackish with age; lamellulae in two to three series.
Stipe 1.0-1.5 cm long, 1-3 mm thick, hollow, straight to bent, more or less equal; surface glabrous, pale-grey at apex, becoming greyish-brown towards the base, surrounded by grey tomentum; partial veil absent.
Spores 6.5-9.0 x 3.5-5.0 µm, elliptical-oblong in face-view, elliptical to tear-shaped in profile, smooth, thin-walled, hilar appendage not conspicuous, inamyloid; spore deposit not seen.
Solitary or in small groups on bare soil, occasionally in moss in montane regions; fruiting in the spring; occasional to common in its preferred habitat.
Unknown; too small to have culinary value.
This small, omphaloid mushroom, also known as Clitocybe atrobunnea, is easily overlooked, its drab color closely matching the soils on which it often fruits, a feature reflected in the species epithet. Arrhenia obscurata is recognized by a dark-brown, appressed-fibrillose, often infundibuliform cap, and strongly decurrent gills. In California it is most likely to be confused with the similarly colored Arrhenia epichysium. The latter, however, occurs only on decayed wood