Agaricus leucolepidotus

Agaricus leucolepidotus L.J. Chen & R.L. Zhao

Index Fungorum number: IF 570204; Facesoffungi number: FoF 01202

Pileus 43–78 mm in diam., 5 mm thick at the disc, hemisphaerical to convex, then becoming applanate-convex, finally applanate, with a slightly depressed centre; cuticle exceeding the lamellae; surface dry, fibrillose, with fibrillose squamules near the margin, white; margin decurved. Lamellae free, crowded, intercalated with lamellulae, 6 mm broad, at first white, pink, then pinkish brown, finally dark brown. Stipe 94 × 8–10 mm, cylindrical with subbulbous base, hollow, white, surface smooth above the annulus, fibrillose woolly below the annulus, not staining on touching. Annulus superous, simple, at middle of stem, upwards, membranous, thickening towards the edge, upper side surface smooth, lower side surface fibrillose. Context firm, on cutting white in both pileus and stipe, not discolouring on exposure. Odour light of almonds. (Fig. 2 i–j) Macrochemical reactions: KOH reaction no discolouration, Schäffer’s reaction negative.

Basidiospores (5.8–) 6.5–7.2 (−8.8)× 3.5–4.3 (−5) μm, [x = 6.8 ± 0.29 × 3.8 ± 0.27, Q= 1.60–2.07, Qm= 1.77 ± 0.01, n = 20], ellipsoid to oblong, brown, smooth, thick-walled, without germ pore. Basidia 13.5–16× 8–10 μm, broadly clavate, hyaline, smooth, 4- or 2-spored. Cheilocystidia 14–21× 9–12.5 μm, abundant, simple, subglobose to pyriform, hyaline, smooth. Pleurocystidia absent. Pileipellisa cutis composed of hyphae 3–9 μm in diam., cylindrical, hyaline, smooth, and at times slightly constricted at the septa (Figure 3).

Habitat: in groups, in forest clearings. Known only in Thailand.

Material examined: THAILAND, Chiang Mai Prov., Tharnthong Lodge, 31 May 2012, collector Jie Chen, LD201214 (MFLU12-0858, holotype; HMAS273995, isotype)

Notes: This new species is morphologically similar to A. albosquamosus in the field in having a white and squamosa pileus (see the above, the new species proposed in this paper); however, it has larger basidiospores. In ITS, they differ by 5 base pairs.

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.