The type was collected on dead culms of Scirpus holoschoenus. Also found in moss, on buried twigs, on roots of Rubus sp. and needles of Abies alba. Summer to autumn. Recorded in Spain, Italy, France and Norway.
Pileus 6-20 mm across, conical to conical-campanulate, becoming convex with age, shallowly sulcate, translucently striate, dry, slightly hygrophanous, entirely white-puberulous or pruinose, glabrescent, very pale brown to light grey, darker at the centre. Lamellae 15-27 reaching the stipe, ascending, adnate to broadly adnate, decurrent with a small tooth, white to greyish to grey-brown, lamellar edge concolorous or paler. Stipe up to 60 x 2.5 mm, hollow, terete, equal or very slightly wider towards the base, fragile, densely white-greyish puberulous in the entire length, pale brown to greyish brown, sometimes becoming very dark grey to black at the base when drying, the base covered with short to long, coarse, whitish fibrils. Odour indistinctive to nitrous.
Basidia 20-37 x 7-9 µm, clavate, 4-spored, with sterigmata up to 8 µm long. Spores 8-10.5 x 4.5-6 µm, q = 1.4-1.9, qav = 1.7, pip-shaped to subcylindrical, smooth, amyloid. Cheilocystidia 26-70 x 8-18 µm, forming a sterile band, smooth, clavate, fusiform, sublageniform to cylindrical, rarely subpyriform (a few more irregularly shaped with somewhat furcate apex). Pleurocystidia similar if present. Hyphae of the pileipellis 2- 4 µm wide, densely covered with short to long, simple to branched, straight to curved, cylindrical excrescences up to 35 x 1.5-3 µm, not embedded in gelatinous matter. Lamellar trama dextrinoid. Hyphae of the stipitipellis 1.5-5.5 µm wide, smooth or with some isolated thick excrescences 3-10 x 2-3.5 µm, terminal cells somewhat inflated and coarsely diverticulate; stipitipellis covered with long, curved to flexuous ‘hair-like’ caulocystidia, up to 300 x 1-5 µm, with somewhat swollen base with slightly thickened walls, tapering towards the apex, simple to furcate and sometimes with lateral excrescences. Clamp connections generellay present, but see remark below.
Mycena scirpicola is a member of section Fragilipedes (Fr.) Quél. In the field it could be mistaken for Mycena leptocephala (Pers.) Gillet. The densely puberulous stipe, caused by very long, slender, hair-like caulocystidia separates it from the former species. In the literature seven Mycena species of sect. Fragilipedes have been described producing hair-shaped caulocystidia. They are Mycena bambusae-pygmaea Robich, M. cretata Aronsen, M. pilosella Maas Geest., M. pruinatipes Robich, M. scirpicola M. Villarreal, Heykoop, Esteve-Rav. & Maas Geest., M. spinulosipes Robich, and M. villicaulis Maas Geest. The differences between these taxa are rather minor and not fully understood (see Aronsen 2009), and the intraspecific variation may be greater than indicated by the type descriptions. It would seem that this group is in great need of molecular studies.
The Norwegian record was earlier given the provisional name Mycena prospera. It differed from the type description of M. scirpicola in several aspects: only 14 lamellae reaching the stipe, pleurocystidia present, the caulocystidia somewhat shorter (-150 µm long), odour nitrous, and the stipe not darkening when drying. Examination of a French account, kindly put to my disposal by Dr. H. Cochard, however, has convinced me that the Norwegian record fits within the variation of M. scirpicola.
M. scirpicola was described as a species possessing clamp connection. This matches both the Italian (Robich 2003) and the Norwegian record. The French record, however, was devoid of clamps. This phenomenon is known also in the close ally M. leptocephala, that can be encountered both with and without clamps.