Agaricus angusticystidiatus M.Q. He, Desjardin, K.D. Hyde & R.L. Zhao
Pileus 40–80 mm diam., plano-convex, applanate, broadly umbonate; surface concentric squamulose with small skull-cup at disc, appressed, slightly fissured, light brown (6D8), brown (7E3), greyish-brown (5D5), dark brown (6D6) against the grey (8E3) background. Context 4–5 mm thick at disc, fragile, white to grey (8E3) in age. Lamellae free, crowded, lamellulae with 3–4 lengths, 3–4 mm broad, normal to slightly ventricose, brown (7E5) to dark brown (7F7-8), edge colour similar to the gill itself. Stipe 55–100 × 5–8 (base 8–15) mm, cylindrical bulbous, with rhizomorphs in most cases, hollow, surface glabrous to silky, white to dark brown (6D6). Annulus pendent or percurrent; single; upper side membranous, white; lower side surface powdery, light yellow (4B2) grain-like dots in circulate; superior, persistent, edge entire, up to 5 mm broad. Smell of iodoform. No colour change on touching; light dull red, greyish brown (7D4) on cutting.KOH reaction: negative. Schäffer’s reaction: negative on dry specimens. Basidiospores 5–6.5 × 3–4 (–4.5) µm [X = 5.6 ± 0.5 × 3.8 ± 0.4, Q = 1.1–2.2, Qm = 1.52 ± 0.7, n = 20], cymbiform, some endosporium, no germ pore, brown. Basidia 10–15 × 5.5–7 µm, clavate, hyaline, smooth, 4-spored. Pleurocystidia absent. Cheilocystidia 20–30 (–45) × 5–8 µm, occasionally one septum, narrowly clavate to clavate, some with elongated top, rarely subcapitate, hyaline, smooth. Pileipellis cutis consisting of 3–5 µm diam. hyphae, hyaline, smooth, non-constricted at septa. Annulus hyphae same as pileipellis. (Fig. 2)
Etymology: refers to the narrow clavate cheilocystidia.
Holotype: Thailand, Chiang Mai Province, Mae Taeng, Baan Mae Sae village, on Hwy 1095 near 50 km marker, 19°14.599'N, 98°39.456'E, alt. 960 m. In rain forest dominated by Castanopsis armata, Castanopsis sp., Pinus sp., Lithocarpus sp., 26 June 2005, collected by Jennifer Kerekes. Holotype: ZRL2043 (HMAS279593); Isotype: BBH19428 and SFSUZRL2043
Habitat: Gregarious on soil in rain forest which is mainly dominated by Castanopsis armata, Castanopsis sp., Pinus sp., Lithocarpus sp.
Specimen examined: THAILAND, Chiang Mai Province, Mae Taeng, Baan Mae Sae village, on Hwy 1095 near 50 km marker, 19°14.599'N, 98°39.456'E, alt. 960 m. In rain forest dominated by Castanopsis armata, Castanopsis sp., Pinus sp., Lithocarpus sp., 26 June 2005, collected by Jennifer Kerekes. Holotype: ZRL2043 (HMAS279593); Isotype: BBH19428 and SFSUZRL2043. Thailand, Chiang Mai Province, Mae Taeng, Ban Mae Sae Village, on Hwy 1095 near 50 km marker, 19°14.599'N, 98°39.456'E, elev. ca. 960 m, 3 July 2004, collected by Thitiya Boonpratuang, ZRL2085 (HMAS279594, BBH19468 and SFSUZRL2085); Thailand, Chiang Mai Province, Mae Taeng, Mushrooms research center, 30 July 2014, collected by Boontiya Chuankid, BC088 (MFLU 14-0903).
Distribution: Thailand, Chiang Mai Province (type distribution)
Notes: This new species is morphologically distinguished from other Agaricus species by its strong iodoform smell, context reddish-brown discolouration on cutting, cymbiform basidiospores and narrow cheilocystidia with variable shapes. Phylogenetic analyses confirmed it is a member of the subgenus Pseudochitonia with an isolated phylogenetic position in Agaricus.
Fig. 1 Phylogenetic tree of Agaricus subgenus Pseudochitonia generated from Bayesian analysis of ITS sequences, rooted with A.campestris. Bayesian posterior probability (PP) values ≥ 0.9 or Bootstrap support (BS) values ≥ 50% are indicated at the internodes (PP/BS).