Agaricus suthepensis

Agaricus suthepensis L.J. Chen, K.D. Hyde & R.L. Zhao

Index Fungorum number: IF 570206; Facesoffungi number: FoF 01205

Pileus 45–65 mm in diam., 5 mm thick at the disc, convex to hemisphaerical when young, applanate when mature, margin reflexed; surface dry, smooth, with dark-brown triangular squamules, dense at the disc, and sparse near the margin, on a white background, margin decurved. Lamellae free, crowded, intercalated with lamellulae, 3 mm broad, at first white, then pink, reddish brown, and finally dark brown. Stipe 54–114 × 6–7 mm (apex) – 9–14 mm (base), cylindrical with bulbous base, hollow, white, smooth above the annulus, fibrillose below the annulus, staining slightly orange on touching. Annulus simple, membranous, with floccose on lower surface, connected with the stipe by cortinate fibrils, white. Context firm, on cutting white, in both pileus and stipe, discolouration on exposure unknown. Odour mushroomy. Macrochemical reactions: KOH and Schäffer’s reactions negative. (Fig. 2 a–b)

Basidiospores 5–6 × 2.4–3.3 μm [x = 5.5 ± 0.3 × 2.9 ± 0.3, Q= 1.7–2.2, Qm=1.9 ± 0.2, n=20], ellipsoid, brown, smooth, thick-walled, without germ pore. Basidia 13–18 × 6–8 μm, clavate, hyaline, 4-spored. Cheilocystidia absent. Pleurocystidia absent. Pileipellis a cutis composed of hyphae 3.3–14 μm in diam., smooth, obviously constricted at the septa, hyaline or light brown, branched. (fig. 3)

Habitat: scattered in forests. Known only in Thailand.

Material examined: THAILAND, Chiang Mai Prov., Doi Suthep, 16 July 2012, collector Komsit Wisitrassameewong LD2012100 MFLU12-0938, holotype; HMAS273993, isotype). Thailand, Chiang Mai Prov., Doi Suthep, 20 June 2010, collector Komsit Wisitrassameewong, NTT042 (MFLU10-1478).

Notes: This new species has negative KOH and Schäffer’s reactions, lacks cheilocystidia, and stains orange on bruising, which are distinctive characters in this section.

Fig. 1 Phylogeny of Agaricus subgenus Spissicaules generated from Bayesian analysis of ITS sequences, rooted with A. campestris. Bootstrap support (BS) values > 50 % and Bayesian posterior probability (PP) values > 80 % (or >50% in some main clades) are given at the internodes (PP/BS). BT^ means the sequence is from type specimen; a clade with thick branch is corresponding a certain section in Fig. 1.