Agaricus sunanensis R.L. Zhao & B. Cao, in Cao et al., Fungal Diversity 132: 509 (2025)

Index Fungorum number: IF 572242; MycoBank number: MB 572242; Facesoffungi number: FoF 17102; Figs. 1, 2

Etymology – refers to Yugur Autonomous County of Sunan, Gansu Province, China, the locality of the type specimen.

Holotype – HMAS 290957.

Pileus 5–13.5 cm in diameter, at first globose, then plano convex, later truncate and finally applanate with a shallow depression in the middle, white towards the margin, with ochre colors more or less tinged yellowish, irregularly distributed over the pileus. Margin involute, exceeding the lamellae up to 0.5 cm in mature specimens. Lamellae free, crowded, up to 1 cm broad, at first whitish, then reddish brown, finally blackish. Stipe usually 4–7.5 × 1.5–3 cm, central, cylindrical, base at times slightly bulbous, with one or two annuli, smooth in above the upper annulus, and furfuraceous scales below the lower annulus. Annulus inferous, one or double, membranous, thick, fibrillose upper surface, striate towards the margin on the underside. Context firm on cutting first white, then grayish-brown in the stipe.

Basidiospores (6.1–)6.8–7.4–8.4(–9) × (5.2–)5.9–6.3–7(–7.9) µm, Q = 1.11–1.19–1.24, broadly ellipsoid to subglobose, brown, thick-walled, without germ pore. Basidia 27.1–38.5 × 8.9–13.2 µm, clavate. Pleurocystidia absent. Cheilocystidia hyaline, cespitose, simple or with 1 to 3 septa at the base, terminal element clavate or Pyriform, 18.8–31.2 × 7.6–12.7 µm. Pileipellis a cutis of cylindrical hyphae, slightly constricted at septa, 3.3–9.3 µm wide.

Chemical reactions – Schäffer’s reaction negative.

Material examined – CHINA, Gansu Province, Zhangye City, Yugur Autonomous County of Sunan, 21 August 2017, collected by Ming-Zhe Zhang, QL20170033 (HMAS 290956), QL20170034 (HMAS 290957, holotype), and QL20170208 (HMAS 290983); 22 August 2017, Xin-Yu Zhu, QL20170263 (HMAS 290997).

GenBank – HMAS 290956: PQ628229 (ITS); HMAS 290957: PQ628230 (ITS); HMAS 290983: PQ628231 (ITS); HMAS 290997: PQ628232 (ITS).

Notes – Agaricus sunanensis belongs to Agaricus sect. Bivelares, a group that includes several well-known edible species, such as the cultivated A. bisporus (J.E. Lange) Imbach and A. bitorquis (Quél.) Sacc. Agaricus sunanensis is characterized by its large, robust fruiting bodies and is considered a palatable wild edible mushroom.

Figure 1 – Maximum Likelihood tree of Sect. Bivelares and Bohusia based on ITS sequences, bootstrap values greater than 50% are shown around nodes. New species are shown in blod. “T” refers to a type specimen.

Figure 2 – Agaricus sunanensis (HMAS 290957, holotype). a, b Basidiomata. c Basidiospores. d Basidia. e Cheilocystidia. f Pileipellis hyphae. Scale bars: a, b = 2 cm, c–f = 10 µm.