Scattered to gregarious on the decaying rachis of the fronds of diverse ferns. Summer to autumn. Widely distributed. Common in Norway.

Pileus 1.5-3(-5) mm across, almost cylindrical to conical, slightly depressed centrally, very shallowly sulcate, translucent-striate, pruinose, glabrescent, pale pink, sometimes very pale brown at the centre, beige to white at the margin. Lamellae 5-11 reaching the stipe, ascending, broadly adnate, decurrent, white, the edge concave, pink. Stipe 10-30 x 0.2-0.3 mm, terete, straight to flexuous, equal, glabrous, at first black at the apex and grey down towards a pink base, then pink to whitish, the base somewhat bulbuous, attached with radiating, white fibrils. Odour none.

Basidia 20-27 x 8-10 μm, broadly clavate, 4-spored. Spores (7.5-)9.5-12.5 x 4-5 μm, Q 1.9-2.5, Qav 2-2.2, pip-shaped, smooth, amyloid. Cheilocystidia 20-40 x 7-20 μm, forming a sterile band, clavate to obpyriform, with reddish contents, covered with fairly numerous, simple, rarely furcate, cylindrical excrescences of unequal length 2-13.5 x 0.5-1 μm. Pleurocystidia absent. Lamellar trama dextrinoid, brownish vinescent in Melzer's reagent. Hyphae of the pileipellis 2-10 μm wide, densely covered with warts or short cylindrical excrescences 0.5-2 x 0.5 μm, terminated by cystidia at the margin of the pileus, similar to the cheilocystidia. Hyphae of the cortical layer of the stipe 2-5 μm wide, densely covered with simple, cylindrical excrescences 1-3 x 0.5-1 μm, the terminal cells not much inflated, densely diverticulate. Clamp connections abundant.

Mycena pterigena has a somewhat isolated position in the genus being the only member of sect. Pterigenae (Maas Geest.) Maas Geest. It should be easy to identify because of the occurence on decaying fern stalks, the small size, the pink colours of pileus and stipe, and the pink coloured lamellar edge. Occasionally some white specimens may be found growing among normally coloured basidiomata. Such specimens do not seem to deserve a rank of form or variety.

Mycena lohwagii, also growing on ferns, has a pale brown to whitish pileus and a larger number of lamellae reaching the stipe. There are many characters that separate it from white specimens of M. pterigena: