In groups on dead, standing culms of Phragmites australis just above the level of stagnant water. Autumn to early winter. Known from Denmark and Sweden, and other European countries, but not yet recorded in Norway.

Pileus up to 20 mm across, at first hemispherical, then plano-convex, soon with depressed centre or becoming umbilicate to infundibuliform, shallowly sulcate, translucent-striate, minutely tomentose when very young, glabrescent and becoming viscid, covered with a separable, tough, gelatinous pellicle, fairly pale grey-brown, dingy yellowish brown, with age turning reddish brown to sepia brown, paler at the centre, finally fading to dingy whitish, the margin at first strongly involute, then straight. Odour variously experienced as indistinctive, agreeable but hard to describe or reminiscent of the smell of Sphagnum. Taste indistinctive or slightly bitter. Lamellae 18-26 reaching the stipe, somewhat elastic, arcuate, up to 3 mm broad, fairly thick, broadly adnate, deeply decurrent, smooth or ribbed, becoming dorsally intervenose, dingy white to very pale sepia brownish, sometimes with a pink flush, the edge concave, not gelatinized, concolorous. Stipe up to 65 x 3 mm, hollow, somewhat elastic, equal for the greater part or somewhat broadened below, terete, straight to curved, smooth, at first minutely but densely white-puberulous all over, glabrescent and becoming somewhat glutinous, pure white in very young specimens, then watery whitish, discolouring pale yellowish brown or pale grey-brown from base upwards, finally with the base dark red-brown or even blackened, the base arising from a thin whitish, mycelial patch, more or less densely covered with white fibrils which may unite to form coarse, radiating, brownish stands.

Basidia 34-44 x 8.5-13 µm, clavate, 4-spored, with sterigmata up to 10 µm long. Spores 10.5 - 15.5 x 6 - 8.5 µm, q = 1.7 - 2.4, qav = 1.99 (29 spores measured), ellipsoid to almost cylindrical, smooth, amyloid. Cheilocystidia 21-55 x 8-14 µm, mixed with the basidia, fusiform or subcylindrica, smooth or with coarse excrescences apically. Pleurocystidia absent. Lamellar trama vinescent in Melzer's reagent. Hyphae of the pileipellis 2-5 µm wide, smooth, embedded in gelatinous matter. Hyphae of the cortical layer of the stipe 1.5-2.5 µm wide, smooth, covered with gelatinous matter, terminal cells subclavate to subcylindrical, somewhat irregularly shaped, smooth or diverticulate. Clamp connections present.

The macroscopic description has been taken from Maas Geesteranus (1989: 478-479). The microscopic notes are based on one Swedish collection (Örstadius/Rydberg, LÖ 503-05). For more microscopic details, see Robich, Forum di Micologica.

Mycena belliae grows exclusively on dead, standing culms of Phragmites australis. As far as I know, it has only been recorded in inland lakes, and not at the sea coast. It occurs very late in the autumn, and can also be found in mild periods in the winter. It seems to grow not very close to the shore, at a water depth of 10 - 50 cm, and up to 12 cm above the water level. When the water is deeper it does not seem to thrive.