Agaricus sodalis L.J. Chen, R.L. Zhao & K.D. Hyde.
Index Fungorum number: IF551000, Facesoffungi number: FoF00477
Pileus 42–90 mm diam., 3.5 mm thick, plano-convex with truncate centre; surface dry, with violet-brown fibrils, densely arranged at disc, rarely distributed or none towards the margin on whitish background; margin finely crenulate; Lamellae free, crowded, lamellulae with 3 series, 2.5–4 mm broad, at first white, then pinkish, later greyish-brown and finally dark brown; lamellae not exceeding the margin. Stipe 40–80×5–9 (10–15 at base) mm, fistulose, cylindrical with a bulbous base, surface white, becoming yellow by handing, smooth above annulus, fibrillose below. Annulus membranous, single, fragile white, turning yellowish on bruising. Context firm, first white, becoming conspicuously yellow when cut. Odour like almond. Microchemical reactions: KOH reaction positive yellow. Schäffer’s reaction is positive reddish-orange. (Fig. 1)
Basidiospores 5–5.6 (–6.2) × (3.2–) 3.4–3.8μm, (x=5.4× 3.6μm, Q=1.39–1.63, Qm=1.50, n=20), ellipsoid, smooth, brown, thick-walled. Basidia 12.5–25×7–8.5μm, clavate, hyaline, smooth, 4-spored; Cheilocystidia 21–38×6.5–14μm, abundant, simple, broadly clavate, pyriform or sphaeropedunculate, with yellowish pigment, smooth. Pleurocystidia absent. Pileipellis a cutis composed of hyphae of 5–12μm diam., cylindrical, rarely branched, hyaline, smooth, constricted at the septa. (Fig. 2)
Habit: gregarious or solitary in open area of forest.
Material examined: THAILAND, Chiang Rai Province, Doi Pui site 2, 31 July 2012, collector Jie Chen, LD2012159 (MFLU 12–0987, holotype), GenBank ITS: KP715161; Chiang Rai Province, Doi Pui site 1, 1 September 2011, collector Benjarong Thongbai, LD2011029 (MFLU 11–1311), GenBank ITS: KP715160.
Notes: The positive KOH and Schäffer’s reactions, the almond-like odour and the simple cheilocystidia, place A. sodalis in Agaricus section Minores. It is characterized by its robust sporocarps, violet brown fibrils on the disc of the pileus surface, but few or none elsewhere on a whitish background, the simple cheilocystidia containing yellowish pigments, generally broadly clavate or sphaeropedunculate in shape and the spores with an average size of 5.4×3.6μm. Within the section, there are few species having robust sporocarps, exceptions are A. brunneolus (J.E. Lange) Pilát, A. megalosporus J. Chen et al. and A. pseudolutosus (G. Moreno et al.) G. Moreno et al. Firstly, A. brunneolus exhibits much more coloured fibrils on the entire pileus surface while the colour can be very variable, from dark reddish purple to white and all the intermediate colour shades, and there is no yellowish pigments been described from its cheilocystidia. The two other species can be differentiated by their larger sized spores (A. megalosporus 6×3.5μm; A. pseudolutosus 6.37×4.78μm); additionally A. megalosporus shows a well coloured fibrillose squamules pileus and a variable shape of cheilocystidia has been observed in A. pseudolutosus. In the phylogenetic analysis, A. sodalis forms a clade with A. huijsmanii and three undescribed species labelled as A. sp. ZRL3101, A. sp. NT62 and A. sp. NTT72, but without significant support.
Fig. 1 Phylogram generated from Maximum Likelihood (PhyML ver 3.0) analysis based on ITS sequences of Agaricus sodalist. Maximum Likelihood bootstrap support values greater than 50 % are indicated above the nodes, and branches with Maximum parsimony bootstrap support values greater than 75 % are given in bold. The type species are given in bold; the new specimens are in blue.