Agaricus purpureofibrillosus Linda J. Chen, R.L. Zhao & K.D. Hyde
Facesoffungi number: FoF 02291; MycoBank MB818055
Pileus 2–3 cm diam, 1 mm thick at disc; at first conical, then convex to plano-convex, finally applanate; surface dry, entirely covered with purplish fibrils, dense at disc and more sparse towards the margin, on a white background; strongly flavescent when margin is bruised. Margin straight, shortly exceeding the lamellae, often with appendiculate remains of the annulus. Lamellae free, crowded, 2 mm broad, with intercalated lamellulae, at first white, then pink, brown when mature. Stipe 36–45 × 3–6 mm, cylindrical fistulose, surface both above and below the ring smooth, silky, white, strongly flavescent when rubbed. Annulus simple, membranous, superous, white, fragile. Context firm, white, flavescent when cut. Odour of almonds. Spores 4.5–5(–5.3) × 2.7–3 µm, (x = 4.9 ± 0.12 × 2.9 ± 0.14 µm, Q = 1.25–1.66, Qm = 1.69 ± 0.02, n = 20), ellipsoid or amygdaliform, smooth, brown, thick-walled. Basidia 16–22 × 6–7 µm, clavate, hyaline, smooth, 4-spored. Cheilocystidia 9–25 × 7–15 µm, abundant, simple or rarely septate at base, pyriform, sphaeropedunculate, or broadly clavate, with yellowish pigments, smooth. Pleurocystidia absent. Pileipellis a cutis composed of hyphae of 6–12.5 µm wide, cylindrical, often with crystalline brownish pigment inside, constricted at the septa. Macrochemical reactions — KOH reaction positive, yellow. Schäffer’s reaction positive, reddish orange on dry specimen. (Figs. 1–2)
Habitat: Solitary, in soil of roadside.
Material examined: Thailand, Chiang Mai Prov., MRC, 10 July 2006, T.H. Li, ZRL3080 (holotype BBH19596; isotype HMAS279145); Chiang Rai Prov., Mae Sae, 28 July 2010, N. Tongklang, NTF063 (MFLU).
Notes: Agaricus purpureofibrillosus is morphologically well characterized by its slender sporocarps, a pileus surface entirely covered with purplish fibrils, small spores and simple cheilocystidia. Among the members of A. sect. Minores, numerous species morphologically resemble A. purpureofibrillosus by sharing a slender sporocarp and purplish fibrillose pileus, such as A. dulcidulus, A. gemlii, A. parvibicolor, and A. purpurellus. However, they can be distinguished on account of the following characters: A. dulcidulus has smaller spores (4.3 × 3 μm on average) and grows under broadleaved trees as Quercus or Carpinus; A. gemlii differs in its larger spores (5.6 × 3.8 μm on average) and the habitat in damp Atlantic environments near the coast; A. parvibicolor, a species recently described from Thailand, differs by the finely striate pileus margin and larger spores (5.2 × 3.3 μm on average); A. purpurellus differs in its wider spores (5.2 × 4 μm on average) and the distinctive habitat in conifer woods. Otherwise, the molecular data is essential for unequivocal identification.