Among fallen leaves of Fagus and firmly attached to these by a dense growth of fibrils, typical in heath forests (low pH). Sometimes fruiting in hundreds and almost forming a carpet on the ground. Autumn. Rare in Norway, but locally common in a few Fagus localities in Vestfold and Agder.

Pileus 10-30 mm across, broadly campanulate to more or less convex, mostly with a low umbo, slightly flattened or depressed centrally, sulcate, translucent-striate, glabrous, lubricous when wet, at very young stages greyish brown with white margin, becoming pale grey brown, darker at the centre, sometimes stained with red-brown spots with age. Lamellae 23-29 reaching the stipe, ascending, narrowly adnate or emarginate, sometimes decurrent with a tooth, rugulose and dorsally intervenose with age, pale grey to brownish. Stipe 30-70 x 1-2 mm, hollow, terete, equal, curved below, cartilaginous, breaking with a snap, pruinose, glabrescent, greyish brown to dark brown with somewhat paler apex, attached to leaves of Fagus with long, white fibrils. Odour indistinctive or farinaceous, often reminiscent of radish after a while.

Basidia 22-28 x 5.5-7 µm, clavate, 4-spored, with sterigmata 4-5.5 µm long. Spores 8-10.9 x 3.5-4.9 µm, Q 1.9-2.8, Qav 2.3, narrowly pip-shaped to almost cylindrical, smooth, amyloid. Cheilocystidia 13.5-40 x 4.5-10 µm, clavate to somewhat irregularly shaped, covered with few, rather coarse, unevenly spaced, simple to somewhat branched, straight or curved or even flexuous excrescences. Pleurocystidia not observed. Lamellar trama dextrinoid. Hyphae of the pileipellis 2-3 µm wide, covered with simple to much branched excrescences which tend to form dense masses. Hyphae of the cortical layer of the stipe 2-3 µm wide, smooth to sparsely diverticulate, terminal cells clavate with excrescences. Clamp connections present at all tissues.

Microphoto of cheilocystidia.

The substrate - fallen leaves of Fagus - is characteristic for this species, but other Mycena species can be found in the same habitat and growing in the same manner (e. g. Mycena galopus). As Smith (1947) put it: "One would not be likely to confuse this species with other gray or cartilaginous Mycenae, but it does lack an outstanding character". From my experience it can be identified on account of the habitat, a cartilaginous stipe, which is usually conspicuously curved below, cheilocystidia with finger-like excrescences, narrow spores, and (mostly) a farinaceous odour. Mycena flavescens sometimes co-occurs but can be identified by the faint yellowish lamellar edge, by having more fragile fruitbodies and in having cystidia covered with warts and short excrescences.

Smooth cheilocystidia, mentioned by Smith (1947: 300) to occur in American material, have to my knowledge not been observed in Europe. Smith also reported M. fagetorum growing on Quercus leaves.

Cheilocystidia

Mycena fagetorum, Aronsen M 19/85, Teieskogen, Nøtterøy, Vestfold 6 Oct 1985

More microscopic features