Pileus 5–20 mm, reniform, broadly convex, expanding to applanate, whitish-grey to greyish, entirely matted-tomentose to matted-appressed fibrillose, fibrils whitish, slightly hygrophanous, not striate. Lamellae with 2–3 tiers of lamellulae, adnexed, ventricose, up to 2.5 mm wide, moderately close, pale greyish at first, becoming greyish-pink, entire margin concolorous. Stipe 1–5 × 0.5–1 mm, strongly reduced, lateral, grey, covered with minutely, pale greyish fibrils, at base with white hairy mycelium. Basal rhizoids present, white. Context thin, unchanging. Odour absent. Taste not distinctive.

Basidiospores 8–10 × 5.5–7 (7.5) µm (x = 9 ± 0.3 × 6.5 ± 0.2 µm), Q = 1.29–1.52, Q = 1.39 ± 0.04, 5–6 (7)-angled, heterodiametric in profile view. Basidia 30–34 × 9–11 µm, clavate, 4-spored, rarely 2-spored, clampless. Lamellar edge fertile. Cheilocystidia, pleurocystidia and caulocystidia absent. Pileipellis a cutis composed of cylindrical hyphae, repent terminal cells (30–) 35–50 × 4–7 µm, cylindrical (or slender subclavate), non-gelatinised wall thin, smooth or minutely encrusted with pale brown pigment. Oleiferous hyphae numerous in pileipellis. Clamp-connections present in the pileipellis.

On decaying stump of Betula sp. in deciduous forest dominated by Betula sp. and Quercus sp.

China. Sichuan Prov.: Kangding County, Mugecuo, ca. 2700 m elev., 30°13'N, 101°83'E, on decaying stump of Betula sp., 4 August 2015, X.L. He (SAAS 1160); on decaying stump of Betula sp., 3 September 2015, X.L. He (SAAS 1828); on decaying stump of Betula sp., 3 September 2015, X.L. He (SAAS 1279; ZT 13608). Xizang Autonomous Region (Tibet): Linzhi County, Kadinggou, ca. 2980 m elev., 29°50'N, 93°25'E, on decaying stump of Betula sp., 25 September 2014, X.L. He (SAAS 1025); Linzhi County, Sejila Mountain, ca. 3600 m elev., 29°35'N, 94°25'E, on decaying stump of Betula sp., 24 September 2014, X.L. He (SAAS 1953).

Entoloma byssisedum var. microsporum closely resembles typical E. byssisedum by its small crepidotoid pale greyish-brown basidiomes whose pileipellis is covered with fine, whitish arachnoid fibrils and lateral, strongly reduced to absent stipe. However, the basidiospores of the Chinese specimens are distinctly smaller as recorded for typical E. byssisedum and, thus, the morphotaxonomic characters correspond well with European collections of E. byssisedum var. microsporum (Noordeloos 2004). The identification is further supported by ITS sequences which demonstrate that the Chinese specimens of E. byssisedum var. microsporum are 99% identical as compared to those reported for European material (KJ001409). It is noteworthy that, in GenBank, there are two sequences labelled “E. byssisedum” (EU784209, KJ001413) which, however, are significantly different. The ITS sequences of the Chinese E. byssisedum var. microsporum are 97% identical to EU784209 but do not correspond with KJ001413. Accordingly, it could be speculated that E. byssisedum var. microsporum and E. byssisedum var. byssisedum actually represent two different species.