China. Yunnan Prov.: Binchuan County, Jizu Mountain, ca. 2700 m elev., 25°58'N, 100°21'E, on stem base of living Castanopsis, 8 September 2015, X.L. He (SAAS 1220, holotype).

KU312122 (ITS), KU534237 (nLSU), KU534474 (RPB2), KU534423 (mtSSU).

gregarium (Lat.), referring to gregarious habit.

Entoloma gregarium resembles the Chinese E. conchatum, but differs by smaller basidiospores.

Pileus 5–10 mm, conchate, broadly convex, pure white, unchanging with age, entirely matted-tomentose to matted-depressed fibrillose, opaque, dry, not hygrophanous, margin not striate. Lamellae adnexed, subdistant to distant, subventricose, up to 2 mm wide, with two tiers of lamellulae, white at first, becoming pale pink, in moist condition with small red droplets at edges. Stipe 1–3 × 0.5–1 mm, strongly reduced, lateral, translucent, covered with minutely, white fibrils, equal, with white basal mycelium. Context white, unchanging, thin. Odour and taste not distinctive.

Basidiospores 7–9 (9.5) × 5.5–7 µm (x = 7.7 ± 0.3 × 6.3 ± 0.3 µm), Q = 1.16–1.47, Q = 1.25 ± 0.04, 5–6 (7)-angled, heterodiametric in profile view. Basidia (26–) 30–34 × 7–10 µm, subclavate, 4-spored, clampless. Lamellar edge fertile. Cheilocystidia, pleurocystidia and caulocystidia absent. Pileipellis a cutis of cylindrical hyphae, terminal cells (25–) 35–60 × 5–10 µm, subclavate or cylindrical (rarely also subfusoid), repent or slightly uplifted, non-gelatinised wall thin, smooth, with inconspicuous plasmatic pigment, subpellis composed of short-celled cylindrical hyphae, 6–14 µm diam. Oleiferous hyphae present in pileipellis. Clamp-connections present in all tissues.

Amongst moss on stem base of living Castanopsis in fagalean forest.

China. Yunnan Prov.: Binchuan County, Jizu Mountain, ca. 2700 m elev., 25°58'N, 100°21'E, on stem base of living Castanopsis, 8 September 2015, X.L. He (SAAS 1493); X.L. He (SAAS 1535).

As compared to other sympatric Chinese species, E. gregarium is unique due to the combination of the following characters viz. persistently white and gregarious basidiomes and small basidiospores.

The aforementioned taxa of Claudopus viz. E. conchatum, E. indocarneum, E. crepidotoides, E. exiguum, E. jahnii, C. minutoincanus, C. pandanicola, E. parasiticum, E. pitereka, C. rupestris and C. viscosus have white basidiomes and, accordingly, are macroscopically similar to E. gregarium. However, E. gregarium is separated from E. conchatum, E. jahnii, C. minutoincanus, E. parasiticum, E. pitereka and C. viscosus by smaller basidiospores; C. rupestris differs by the 4–5-angled basidiospores (Largent et al. 2011; Noordeloos 2004).

Based on macromorphological characters, E. gregarium is difficult to distinguish from E. crepidotoides (Deng et al. 2015); however, the different habitats allow the two species to be discriminated. Additionally, the molecular evidence (Figs 8, 9) of E. crepidotoides and E. gregarium clearly indicate that they are two distinctive species. E. indocarneum is characterised by smooth pileus and presence of mycelial rhizoids (Manimohan et al. 2002). Claudopus pandanicola, originally described from tropical Papua New Guinea, is separated by the striate pileus and the different shape of the basidiospores (7–8 × 6.5–7.5 µm, Horak 1980).