Agaricus variicystis

Pileus 53–75 mm in diam., 1–2 mm thick at disc, convex to hemisphaerical, more or less truncate at the disc; surface dry, smooth, occasionally exhibiting very few squamules, on a brownish grey (7C2) background, close to the margin; margin straight. Lamellae free, very crowded, with intercalated lamellulae, 5–7 mm broad, greyish brown to dark brown. Stipe 64–94 × 4–7 (apex) – 8–11 (base) mm, cylindrical to slightly enlarged towards the base, hollow, white, surface smooth, tomentose close to the base (composed of mycelium), staining greyish orange when bruised. Annulus membranous, simple, fragile. Context firm, on cutting pale white both in pileus and stipe, without discolouring on exposure. Odour of phenol. Macrochemical reactions: KOH reaction positive yellow, Schäffer’s reaction negative. Basidiospores 5.6–6.4 (−6.8) × 3.4–3.8 (−4.1) μm, [x = 6.1 ± 0.26 × 3.6 ± 0.17, Q = 1.47–1.78, Qm = 1.66 ± 0.04, n = 20], ellipsoid to fusiform, brown, smooth, thick-walled, endospore thickening, without a germ pore. Basidia12–15.5 × 6–6.5 μm, clavate, hyaline, smooth, 4-spored. Cheilocystidia 20– 55 × 10–23 μm, abundant, variable in shape, rarely pyriform or broadly clavate, often lageniform to utriform, hyaline, smooth. Pleurocystidia absent. Pileipellis a cutis composed of hyphae 4–10 μm in diam., cylindrical, hyaline, smooth, sometimes slightly constricted at the septa. (Figs. 1–2)

Index Fungorum number: IF 570198, Mycobank: 570198, Facesoffungi number: FoF01179

Etymology: epithet “variicystis” refers to variable shapes of cheilocystidia in this species.

Holotype: THAILAND, Chiang Mai Prov., 3 km down the road from Tharnthong Lodges, 4 June 2012, collector Jie Chen, LD201234 (MFLU12-0878, holotype ; HMAS273996, isotype).

            Habitat: scattered or in groups, in soil under the bamboo woods or in forest clearings.

Specimens examined: THAILAND, Chiang Mai Prov., 3 km down the road from Tharnthong Lodges, 4 June 2012, collector Jie Chen, LD201234 (MFLU12-0878, holotype ; HMAS273996, isotype). THAILAND, Chiang Mai Prov., 3 km down the road from Tharnthong Lodges, 4 June 2012, collector Jie Chen, LD201228 (MFLU 12-0872; HMAS273951).