Cap 3.0-11.0 mm broad, convex-depressed, becoming umbilicate to infundibuliform in age; margin incurved, decurved at maturity. surface faintly pruinose when young (use hand-lens), soon glabrous, translucent-striate, sometimes appearing ribbed, dull orange-brown to tawny-brown, hygrophanous, fading to buff or tan; context thin, colored like the cap; odor and taste mild.
Gills decurrent, subdistant, cream-colored; lamellulae up to two-tiered, intervenose.
Stipe 0.7-4.0 cm long, 0.5-2.0 mm thick, more or less equal to slightly swollen at the base, fragile, slender, hollow at maturity; surface pruinose, then glabrous, yellowish-tan to buff; partial veil absent.
Spores 4.0-5.5 x 2.0-2.5 µm, elliptical, smooth, thin-walled, inamyloid; spore print white.
Solitary, scattered to gregarious in mosses; fruiting spring and fall; common.
A diminutive moss-dweller, Rickenella fibula is recognized by a yellowish-orange, striate, umbilicate cap, decurrent, well-spaced gills, and relatively thin, long stipe. It is a common and widely distributed species, but rarely collected because of its size. The cap shape and decurrent gills is suggestive of Xeromphalina and Omphalina. Xeromphalina species, however, can be separated by their lignicolous habit, and dark, thin stipes, often with orange-brown hairs at the base. The primary difference between Omphalina and Rickenella is microscopic, the former lacking pileocystidia, but present in Rickenella, and the reason the cap sometimes appears pruinose with a hand-lens. Also compare with members of the Galerina atkinsoniana complex, ubiquitous in moss beds, similar in size and color, but with a convex cap, adnate, not decurrent gills, and brownish spores.