Solitary, gregarious to cespitose in leaf humus, among
herbs, under shrubs or deciduous trees, less frequently
under conifers, often in fairly moist habitats. Summer to autumn. Not uncommon in alpine Salix shrubs. Widespread, but uncommon. Probably overlooked, and considered to be increasing in Drenthe, the Netherlands (Arnolds et al. 2015). Occasional in south Norway, but also recorded in Finnmark.
Pileus 5-20 mm across, hemispherical to campanulate or parabolical, without or with slight umbo, occasionally somewhat depressed centrally, flattening with age, becoming plano-convex, more or less sulcate, translucent-striate, hygrophanous, delicately rugulose to smooth, glabrous, slightly glutinous when wet, variably coloured, very dark dingy purplish brown to pinkish when young, then becoming pale date brown or yellowish brown with a lilaceous or pinkish tint or entirely pinkish, with concolorous or paler margin. Flesh thin, fragile, watery brownish, with some violaceous tint which gradually disappears. Odour raphanoid. Taste raphanoid. Lamellae 18-31 reaching the stipe, at first arcuate, then almost horizontal, up to 5 mm broad, fairly thick, broadly adnate, decurrent with a tooth, smooth to ribbed, dorsally intervenose with age, at first greyish violet or pinkish grey, gradually turning more brownish with some lilaceous tint, the edge concave to straight or somewhat convex, uneven to eroded or crenate, more or less concolorous with the lamellar face. Stipe 25-65(-90) x 1-2.5 mm, hollow, fragile to firm, equal or somewhat broadened below, straight to somewhat flexuous or curved below, terete, smooth, pruinose to floccose-puberulous above, glabrous farther down, at first fairly dark violet with a slight brownish shade, becoming rather pale lilaceous brown to pale dingy flesh-coloured, the base sparsely covered with long, coarse, whitish fibrils.
Basidia 22-27 x 6.5-7 μm, clavate, 4-spored. Spores 6-9 x 3.5-4.5 μm, Q 1.4-2, Qav 1.6-1.7, pip-shaped, smooth, non-amyloid. Cheilocystidia 30-80 x 6-12.5 μm, forming a sterile band, clavate, subcylindrical, subfusiform, smooth, apically obtuse or (more rarely) mucronate. Pleurocystidia absent. Lamellar trama dextrinoid, Hyphae of the pileipellis 1.5-4.5 μm wide, smooth, lower layers embedded in gelatinous matter. Hyphae of the cortical layer of the stipe 2-3.5 μm wide, smooth, terminal cells (caulocystidia) 27-62 x 6-12.5 μm, clavate fusiform, smooth. Clamp connections present in all tissues.
Microphotos of cheilocystidia
Microphotos of cheilocystidia
Mycena pearsoniana is a member of sect. Calodontes (Fr. ex Berk.) Quél. subsect. Violacellae Singer ex Maas Geest., where it in Europe takes place as the only species. It is separated from the other species in sect. Calodontes on account of the non-amyloid spores and absence of pleurocystidia. The rare species M. kuehneriana is quite similar but has amyloid spores. M. pearsoniana is caracterized by the pinkish to lilaceous brown colours, decurrent lamellae, raphanoid smell and taste, non-amyloid spores, and absence of pleurocystidia.
Harder et al. (2010) showed that the Mycena pearsoniana morphospecies might harbour two phylogenetic species in Europe. This observation was followed up by Harder et al. (2011), where the authors referred to phylogenetic analyses of 91 ITS sequences of both European and North and South American Calodontes collections. (See also Harder et al. 2012). Their analysis showed that European collections identified as M. pearsoniana fall into two sibling clades together with both inamyloid and weakly amyloid North American collections. This result indicates that the inamyloidity of the spores in M. pearsoniana may not be of that high taxonomic value as earlier believed. The spores in some collections may show a weak amyloid reaction after some 40 minutes.