Agaricus leucocarpus Linda J. Chen, Callac, R.L. Zhao & K.D. Hyde
Facesoffungi number: FoF 02282.
Pileus 2.5–4 cm diam, 1–3 mm thick at disc; at first parabolic, becoming hemispherical to plano-convex, finally applanate; surface dry, smooth, completely white with light brownish or ochre tinges at the disc. Margin straight, not exceeding the lamellae, often with appendiculate remains of the annulus. Lamellae free, crowded, 3 mm broad, ventricose, with intercalated lamellulae, at first white, turning pinkish when touched, then pink to greyish brown, finally brown. Stipe 40–65 × 2–5 mm (5–9 mm at base), cylindrical with a subbulbous base, fistulose, surface smooth both above and below the annulus, white, flavescent when rubbed or by handing. Annulus simple, superous, membranous, white, fragile. Context firm, white, unchanging when cut. Odour of almonds.
Spores (4.3–)4.5–5 × 3–3.5µm,(x = 4.7 ± 0.17 × 3.2 ± 0.12 µm, Q = 1.32–1.61, Qm = 1.48 ± 0.02, n = 20), ellipsoid, smooth, brown, thick-walled. Basidia 11–14 × 6.5–8 µm, broadly clavate, hyaline, smooth, 4-spored. Cheilocystidia (11–)18.5–26 × 6–15 µm, simple, pyriform or broadly clavate, hyaline, smooth. Pleurocystidia absent. Pileipellis a cutis composed of hyphae of 4–8 µm wide, cylindrical, not or slightly constricted at the septa, hyaline. Macrochemical reactions — KOH reaction positive, yellow. Schäffer’s reaction negative on dry specimen. (Figs. 1–2)
Habitat: Solitary on soil, in grassland of roadside; or scattered on leaf litter mixed with compost.
Material examined: THAILAND, Chiang Rai Prov., Mae Fah Luang University gate, 27 July 2015, J. Chen, LD201507; Chiang Mai Prov., Tharnthong Lodges, 31 May 2012, J. Chen, LD201215 (holotype MFLU12-0859); Chiang Mai Prov., Tharnthong Lodges, 3 June 2012, J. Chen, LD201226 (MFLU12-0870); Chiang Rai Prov., Bandu, 31 July 2011, S.C. Karunarathna SCK089 (MFLU11-1283).
Notes — Agaricus leucocarpus is a species morphologically well characterized by its slender, pure white sporocarps, with a brownish tinge at disc, small spores and simple cheilocystidia. Considering its morphology, discoloration when rubbed and the almond smell, it is very likely to be a member of A. sect. Minores