Agaricus nigrogracilis R.L. Zhao, 2016

Zhou, Jun-Liang, Su, Sheng-Yu, Su, Hong-Yan, Wang, Bo, Callac, Philippe, Guinberteau, Jacques & Zhao, Rui-Lin, 2016, A description of eleven new species of Agaricus sections Xanthodermatei and Hondenses collected from Tibet and the surrounding areas, Phytotaxa 257 (2), pp. 99-121 : 118

Agaricus nigrogracilis R.L. Zhao , sp. nov. ( Fig. 6 : G–K)

MycoBank NO.: MB 812317

Diagnosis: this species can be recognized by its small basidiomata, pileus covered with brown squamulose, and stiped surface that is white fibrillose to fibrillose squamulose. No discoloration occurs on cutting, and elongated basidiospores are present (5.2–5.9 × 2.9–3.4 μm).

Etymology: the word “nigrogracilis ” refers to the black squamules on the pileus and slender habit; from ‘nigrare’ (Latin) be black, and ‘gracilis’ (Latin) slender.

Material examined: China, Yunnan Prov., Kunming, Yeya Lake Forest Park, N 25°07′15″, E 102°51′47″, elevation 2078.94 m, 30 June 2012, Rui-Lin Zhao (ZRL2012014, HMAS 275735, HOLOTYPE).

Pileus 35 mm in diam., convex to plano-convex; surface innately fibrillose, becoming appressed squamulose towards the margin, brown (oac 662) with a white background; edge decurved. Context 3 mm thick at the disc, white and fleshy. Lamellae free and crowded; 4–5 series of plural-lamellulae, 4 mm broad, pink to brown; edge entire. Stipe 5 mm (apex)– 10 mm (base) × 75 mm (length); long clavate, surface white, dry, silky, and fibrillose to fibrillosesquamulose; hollow. Annulus single, membranous, subperonate, 2.5 mm in diam., with a distinct brown edge; upper and lower surfaces smooth and white. Odor not iodine-like, but pleasant. Changing slightly yellow on touching the surface of the stipe; not discoloring on cutting.

Macrochemical reactions KOH reaction no change or slightly reddish. Schäffer’s reaction negative.

Basidiospores ( Fig. 6-G ) (4.6) 5.2–5.9 × 2.9–3.4 μm [x = 5.4 ± 0.3 × 3.2 ± 0.1 μm, Q = 1.5–2.0, Qm = 1.7 ± 0.1, n = 20 basidiospores]; elongated and occasionally ellipsoid, smooth, thick-walled, and brown. Basidia 13.1–16.4 × 4.5– 5.9 μm, hyaline, smooth, clavate, and 4-spored. Cheilocystidia not observed. Pleurocystidia absent. Pileipellis ( Fig. 6-H ) a cutis composed of hyphae 3.2–7.8 μm wide, cylindrical, branched, and smooth, some of which are constricted at the branch and contain light brown vacuolar pigments. Annulus composed of hyphae 2–6 μm in diam., smooth, long clavoid, hyaline and branched, not constricted at septa; hyphae of the annulus margin contained brown to dark brown vacular pigments.

Habitat solitary in forest.

Notes: Molecular analysis based on ITS sequence indicates that this is a distinct species in section Xanthodermatei ; however, the phylogenetic analysis using multi-gene sequences suggests that this species is a member of section Hondenses . We performed the sequencing and analysis a second time with the same results, such that we were unable to clearly place this species in any section. Correspondingly, the morphology of this species was also quite different from that of the known species in those sections: it lacked color changes after flesh exposure and had a pleasant odor and a negative KOH reaction. Agaricus bukavuensis is a species lacking a color change on cutting, but it has a bulbous stipe and larger basidiospores (5.4–6.9 × 4–4.9 μm) than those of A. nigrogracilis ( Heinemann & Goossens-Fontana 1956, Heinemann 1978).

Figures

FIGURE 6. A–F. Morphology of A. melanocapus (ZRL2011037 HOLOTYPE): A–D Basidiomata, C shows yellow staining at the base of stipe; E. Basidiospores; F. Pileipellis hyphae. G–K. Morphology of A. nigrogracilis (ZRL2012014 HOLOTYPE): G. Basidiospores; H. Pileipellis hyphae; I–K. Basidiomata. Scale bar A–D = 20 mm; I–K = 10 mm; E–H = 10 μm.