Solitary, gregarious or fasciculate on litter or among moss and dead wood in both coniferous and broad-leaved forests, also found under Alnus at a latitude of 2000 m. (Robich 2003). Autumn. One Norwegian record.
Pileus 10-30 mm across, conical to convex-campanulate, translucent-striate near the margin, pruinose, glabrescent, cream to somewhat yellowish white, the margin usually purer white, but also said to be more yellow. Odour none when fresh, of iodoform on drying out. Lamellae 18-34 reaching the stipe, ascending, narrowly adnate, decurrent with a short tooth, white, turning yellowish pink in the herbarium. Stipe 30-70 x 1.5-2.2 mm, hollow, equal, straight, curved below, smooth, glabrous, watery white, at the base covered with fibrils.
Basidia 25-29 x 6-8 µm, clavate, 4-spored. Spores 8-9(-10) x 4.5-5.2 µm, Q 1.5-2, Qav ~ 1.7, pip-shaped, smooth, amyloid. Cheilocystidia 15-35 x 7-19.5 µm wide, forming a sterile band, clavate to obpyriform, covered with comparatively few, fairly evenly spaced, straight or somewhat curved, cylindrical excrescences, some of which are apically capitate, 1-6 x 1-1.5 µm. Pleurocystidia absent. Lamellar trama dextrinoid. Hyphae of the pileipellis 2-3.5 µm wide, somewhat gelatinized and forming dense masses, densely diverticulate, excrescences 1-2 x 0.5-1 µm, frequently also covered by small, almost globose cells 4-9 µm wide. Hyphae of the cortical layer of the stipe 1.5-5 µm wide, not very densely covered with short, fine excrescences. Clamp connections present in all tissues.
The description is based on Kühner (1938), Robich (2003) and one Norwegian collection.
Because of the yellowish-white pileus and stipe, M. xantholeuca is looking quite similar to M. flavoalba, but the latter differs in having non-amyloid spores, smooth, fusiform cheilocystidia and pleurocystidia, and variously shaped, smooth caulocystidia. M. xantholeuca is a member of sect. Filipedes and can be distinguished from the other species in the section on account of the yellowish white pileus in combination with the odour of iodoform on drying out, absence of pleurocystidia, and cheilocystidia covered with conspicuously capitate excrescences
Esteve-Raventós & Moreno (1985) stated that the colour of the pileus in M. xantholeuca can be quite variable, from entirely white to more yellowish white, they did not notice any smell of iodoform, neither in fresh material nor in exciccates. They also stressed the similarity to Hemimycena lactea (Pers.: Fr.) Singer. This species can easily be told apart on account of non-amyloid spores and smooth, often somewhat capitate cystidia.
Norwegian record: NORD-TRØNDELAG: Grong, Sanddøla vis à vis Mortenslund 19.9.1981, on Ulmus, leg. S.Dunfjeld & S. Sivertsen.
Microphoto of the cheilocystidia
Microphotos of the hyphae of the pileipellis