Growing solitary to subcespitose on dead coniferous wood, particularly on much decayed Picea stumps, but also among tall mosses or Sphagnum on woody debris. Also found on fallen, buried cones of Picea. Ocurring in the spring, from ultimo April to the middle of June; mostly found in May. Found in many of the countries covered, including the UK. Red listed in Belgium. Widespread in southern part of Norway, but not recorded north of Trøndelag. Regular and not uncommon in Vestfold and Østfold.

Pileus 10-45 mm across, acutely conical to broadly rounded, with age often becoming plano-convex to applanate, often with an umbo and recurved margin, translucent-striate and sulcate, often conspicuously white-pruinose, glabrescent, not lubricous when wet, almost black-brown when young, then dark sepia brown, paler with age, the outermost margin paler. Lamellae 15-30 reaching the stipe, ascending, narrowly adnate, sometimes becoming veined and dorsally intervenose, whitish to grey. Stipe 30-140 x 2-3 mm, hollow, equal, terete, smooth, pruinose, glabrescent except for the apex, apically dark steel blue in very young specimens, gradually fading, becoming entirely dark brown or whitish above, brown below, the base covered with coarse, whitish fibrils, not infrequently deeply rooting in decayed wood. Odour pronouncedly nitrous. Taste unpleasant, astringent.

Basidia 28-51 x 7-12.5 µm, slender-clavate, 2-spored. Spores 9-15(-17.5) x 7-10(-11) μm, Q 1.4-1.7, Qav ≈ 1.5, broadly pip-shaped, smooth, amyloid. Cheilocystidia 20-73 x 7-20 μm, forming a sterile band, clavate, lageniform, fusiform or somewhat irregularly shaped, apically rounded or narrowed into a simple or furcate neck, or covered with several coarse excrescences 2-20 x 0.5-2 µm; the more intricate excrescences usually situated near the margin of the pileus, where as the cheilocystidia are more smooth in the middle of the lamella. Pleurocystidia scattered, fusiform. Hyphae of the pileipellis 2-5 µm wide, slightly gelatinized, covered with simple to branched excrescences 1.5-20 x 1-2.5 µm. Hyphae of the cortical layer of the stipe 2-5 µm wide, +/- somewhat gelatinized, covered with cylindrical excrescences 1.5-9 x 1.5-2 µm, terminal cells up to 4.5 µm wide, variously diverticulate. Clamp connections absent.

Microphotos of cheilocystidia close to the margin of pileus
Microphotos of hyhae of the pileipellis

Microphotos of cheilocystidia
Microphotos of hyphae of the pileipellis-1
Microphotos of hyphae of the cortical layer of the stipe

More microphotos

Mycena silvae-nigrae is a member of the large section Fragilipedes. It is easily recognized as it is a vernal species, occuring in conifer forests. Furthermore it is identified on account of the nitrous smell, the 2-spored basidia, the absence of clamp connections, and the cheilocystidia mostly with coarse excrescences.

Mycena leptocephala has a more greyish pileus. It is often found in the spring, but is generally 4-spored and clamped, and the hyphae of the cortical layer of the stipe are smooth, with conspicuously inflated terminal cells.

Mycena plumipes is another vernal and nitrous-smelling species, growing on fallen, decaying Picea cones. It is also clampless, but 4-spored; the cheilocystidia are different, and the hyphae of the pileipellis and the cortical layer of the stipe are smooth. The terminal cells of the latter are cylindrical, appearing as caulocystidia.

Mycena stipata is also dark brown and with a nitrous odour and occurs on coniferous wood. It is distinguished on account of 4-spored basidia, presence of clamp connections, smaller spores, absence of pleurocystidia, and both hyphae of pileipellis and stipitipellis are +/- smooth and embedded in gelatinous matter. In wet condition it has a more lubricous pileus and stipe.