What You Should Know
Closely related to the better known Mycena adonis, this tiny, beautiful mushroom grows on the ground in hardwood forests, usually in the vicinity of rotting wood. It features a bell-shaped to conical, yellow to a dull orange cap, and a stem that often forms a tap root that burrows into the substrate.
Under the microscope, it has fairly inconspicuous, fusoid-ventricose cheilocystidia and nearly round spores. Mycena roseipallens, which also appear under hardwoods, are nearly identical but have more red in their cap color and feature ellipsoid spores.
Mycena adonis has a more red pileus; the stipe is not rooting nor turning dark brown from the base at age. In addition, the spores are pip-shaped, and the basidia are either 2- spored or 4-spored.
Atheniella leptophylla (Peck) Gminder & Böhning is a synonym.
Mycena leptophylla Mushroom Identification
5-30 mm across, conical to campanulate, expanding to parabolical or convex, with or without an umbo or papillate, delicately pruinose, glabrescent, hardly or shallowly sulcate, translucent-striate, somewhat hygrophanous, ochraceous orange-yellow, vivid orange, orange-brown, paler at the margin, darker, deep orange to brown at the center.
20-26 reaching the stem, adnexed, ±decurrent with a short tooth, becoming dorsally intervenose, cream to pale ochraceous or with an incarnate flush, the edge paler to whitish.
20-80 x 1-2 mm, cylindrical, equal, entirely pruinose to minutely puberulous, at first watery white, turning grayish brown to fairly dark brown from the base, the base mostly extended into a long root, densely covered with whitish fibrils.
24-30 x 7-9 um, clavate, 2- 4- spored on the same lamella, with sterigmata up to 5 um long.
6.8-9.5(-10.5) x 5.5-7.2 um, Q = 1.1-1.4, Qav = 1.3, broadly pip-shaped to citriform to subglobose, with strongly projecting apiculus, non-amyloid.
Cheilocystidia 16-48 x 4-14.5 um, forming a sterile band, fusiform, clavate, subutriform, obovoid, or somewhat irregularly shaped, apically broadly rounded to mucronate. Pleurocystidia similar if present. Lamellar trama not dextrinoid. Hyphae of the pileipellis 1-4.5 um wide, covered with simple to branched, straight to curved, cylindrical excrescences up to 14.5 x 2 um which tend to form dense masses. Hyphae of the cortical layer of the stem 1.5-4 um wide, smooth. Caulocystidia 15-50 x 3.5-8 um, clavate to fusiform, smooth. Clamps are present in all tissues.
Photo 1 - Author: Arne Aronsen, Naturhistorisk museum, Universitetet i Oslo (Creative Commons Attribution-Share Alike 3.0 Unported)