Summary:
Features include small size, a non-viscid striate cap that is bright orange (varying to pale brown) changing to dingy ochraceous or buff, long-decurrent whitish gills, a cap-colored stem that is finely hairy at first, and growth on moss. Rickenella fibula was removed from Mycena and placed in Rickenella because of the non-amyloid spores and the size and location of spores. It is common.

Cap:
(0.3)0.8-1.2(1.5)cm across, "slightly convex, flat or the disc faintly depressed at first, the margin straight or curved in slightly", when old the disc deeply depressed but the margin remaining decurved [downcurved]; bright orange or ochraceous orange, soon changing to sordid ochraceous or buff ("cinnamon buff" to "clay color"), in some collections dull pale brown colors appear from the first and all intergradations occur; moist when fresh, (Smith), 0.3-1.5cm across, "convex with deep depression at center"; orange-yellow to buff; striate, (Phillips) 0.3-1.5cm across, convex to flat, slightly to deeply sunken in center, margin inrolled to straight; ocher-orange to buff; moist, margin lined, (Lincoff), 0.3-1.5cm across, convex with depressed center, margin inrolled at first; "orangish brown to reddish brown, fading to yellowish orange or orangish yellow"; dry to moist, smooth, margin becoming striate to sulcate, (Bessette), with serrated edge, hygrophanous, (Schalkwijk-Barendsen)

Flesh:
very thin, fragile; pale orange to buff, (Smith)

Gills:
long-decurrent, subdistant to close, 17-20 reaching stem, 1 or 2 tiers of subgills, gills narrowed at extremities but broad in the notch between cap and stem, often interveined; white or whitish, (Smith), "deeply decurrent, distant; white", (Phillips), "descending stem, long, close to almost distant, narrow to broad", often with cross-veins; white to buff-white, (Lincoff), white to buff (Schalkwijk-Barendsen), strongly decurrent, distant; whitish, (Bessette)

Stem:
1-4cm x 0.1-0.15(0.2)cm, equal, fragile, hollow; concolorous with cap and fading in the same way; finely pubescent overall from cystidia but becoming bald when old, (Smith), 1-5cm x 0.1-0.2cm, "yellow-orange; smooth to finely hairy", (Phillips), 1-5cm x 0.1-0.15cm, fragile, hollow; ocher-orange to buff; finely hairy at first, (Lincoff), 1-5cm x 0.1-0.2cm, fragile, hollow; yellowish orange to orangish yellow; "dry to moist, very finely hairy at first, becoming smooth", (Bessette)

Odor:
not distinctive (Smith, Phillips)

Taste:
not distinctive (Smith, Phillips)

Microscopic spores:
spores 4.5-6 x 2.5-3 microns, narrowly elliptic, smooth, inamyloid; basidia 4-spored; pleurocystidia and pilocystidia [sic, probably an error for cheilocystidia] scattered to abundant, 36-56 x 6-10 microns, "subcylindric to subfusoid, the apex tending to be more rounded than pointed, at times subcapitate", colorless, thin-walled; cap trama homogeneous, yellowish in iodine, the surface covered with elongated pileocystidia 60-90 x 10-14 microns; caulocystidia abundant near apex of stipe, similar in size and shape to the pileocystidia, (Smith), clamps mentioned for basidia, cap cuticle, (Breitenbach), 4-5 x 2-2.5 microns, elliptic (Phillips, Lincoff, Bessette)

Spore deposit:
white (Phillips)

Notes:
Material was examined from WA, OR, ID, NS, ON, MD, MI, NC, NY, and TN, (Smith(1)). There are collections from BC at the Pacific Forestry Center and the University of British Columbia. R. fibula occurs in CA (Desjardin(6)). It is also reported from elsewhere in North America, and from Europe and Asia.

EDIBILITY

unknown (Phillips), inedible (Bessette)

Synonyms and Alternate Names:
Gerronema fibula (Bull.) Singer
Mycena fibula (Bull.) Kuehner
Omphalina fibula (Bull.) Quel.