On decaying Scirpus and Carex in wet areas. Autumn. Rarely recorded but known from Denmark, Sweden, France, Germany and Norway (Aronsen & Læssøe 2016). Probably rare in Norway, but could have been overlooked because of the special habitat and small size. Listed as DD in The Norwegian Red List (2021).

Pileus 1-4 mm across, hemispherical to convex, ±depressed or papillate, shallowly sulcate, translucent-striate, pruinose, glabrescent, pink to very pale brown with a faint pinkish shade, darker in the centre; the margin very pale, whitish. Lamellae 8-10 reaching the stipe, ascending to subhorizontal, the ege concave, fairly broad, broadly adnate, somewhat decurrent with a short tooth, incarnate to whitish with pure white edge. Stipe 3-25 x 0.2-0.5 mm, cartilaginous, hollow, equal, terete, straight to somewhat flexuous, minutely puberulous, incarnate, whitish or grey, becoming somewhat yellowish from the base with age; the base covered with short, white fibrils. Odour indistinctive.

Basidia 24-27 x 7 µm, clavate, 4-spored. Spores 7.8- 10.5 x 3.8-4.5 µm, Q 1.8-2.5, Qav≈2.2, pip-shaped, smooth, amyloid. Cheilocystidia 18-26 x 7-15 µm, forming a sterile band, clavate or somewhat irregularly shaped, covered with fairly few, more or less unevenly spaced, simple to branched, straight to somewhat curved excrescences 1-7 x 1-1.5 µm. Pleurocystidia absent. Lamellar trama dextrinoid. Hyphae of the pileipellis 3-6.5 µm wide, diverticulate. Hyphae of the cortical layer of the stipe 2-2.5 µm, diverticulate; caulocystidia abundant at the base of the stipe, clavate to subglobose, densely diverticulate. Clamp connections absent.

Mycena riparia belongs to a group of small, pinkish species growing on monocotyledons in wet areas. M. juncicola has been described with a more brownish pileus, somewhat more regularly ornamented cheilocystidia, non-inflated terminal cells of the stipe cortex, and presence of clamps. M. tubarioides can be distinguished by a gelatinous matter covering the hyphae of the pileipellis, arcuate, very broad lamellae with a gelatinous edge, larger spores, and by possessing clamps. The American species M. culmigena Maas Geest. was described as a greyish vinaceous species or with a purplish tinge; with somewhat larger spores, more regularly shaped cheilocystidia, and clamps present.

Mycena riparia is a member of Sect. Polyadelphia Singer ex Maas Geest.

Further images on the web:

Jean-Marc Moingeon