Agaricus megacarpus R.L. Zhao & B. Cao, sp. nov. 2020
Fungal Names: FN 570671
Holotype: CHINA. GANSU: Zhangye, Yanzhi Mountain (38°04′20″N, 101°21′32″E; 2704 m asl), scattered on ground in coniferous forest, 20 Aug 2017, Mingzhe Zhang QL20170178 (holotype HMAS 255459).
Morphological description
Pileus 90–185 mm wide, at first broadly parabolic or hemispherical, then convex with applanate center, and finally applanate with uplifted margin and center slightly depressed; surface dry, at first covered by appressed thick fibrils, then broke into appressed scales, sometimes smooth, white to light brown or light orange tone in age; edge slightly exceeding, at times appendiculate with remnants of the annulus. Lamellae free, up to 5–6 mm broad, crowded, with intercalated lamellulae, at first pink or pinkish brown, finally dark brown. Stipe 85–160 × 20–35 mm, cylindrical to slightly clavate, stout, hollow, white, smooth or slightly fibrillose above the annulus, floccose when young then fibrillose squamose below the annulus, becoming yellowish when bruised. Annulus superior, membranous, fragile and attached at the margin of pileus or entirely at the stipe, smooth and white on the upper surface and floccose and white or with few light brown flakes on the lower surface. Context white, unchanged or becoming yellowish toward the stipe base. Odor of almond. KOH reaction yellow; Schäffer’s reaction reddish orange on pileus and stipe.
Basidiospores (6.5–)7–8 × 5–6 μm [x¯= 7.4 × 5.3 μm, Q = 1.3–1.5, Qm = 1.4, n = 30], ellipsoid or ovoid, smooth, thick-walled, brown. Basidia 24.5–31.5 × 9–11 μm, 4-spored, clavate or slightly truncate at the apex, hyaline, smooth. Cheilocystidia 14–30 × 4–14 μm, hyaline, simple or sometimes catenulate, consisting of obovoid, clavate, or ellipsoid elements. Pileipellis a cutis of cylindrical hyphae, 3–10.5 μm wide, slightly constricted at septa, hyaline.
Habitat: on ground in coniferous (Picea) or broadleaf forest.
Distribution: northern China.
GenBank Accession: ITS MK617861; 28S MK617774; tef1 MK614371
Notes: Agaricus megacarpus is represented by six specimens from Beijing, Hebei, and Gansu in a well- supported clade (96/1.0 BS/PP) (FIG. 1).
Reference: Bin Cao , Mao-Qiang He , Zhi-Lin Ling et al. (2020): A revision of Agaricus section Arvenses with nine new species from China.
Agaricus megacarpus (QL20170178, holotype). A, B. Basidiomes. C. Basidiospores. D. Cheilocystidia. E. Basidia. F. Pileipellis hyphae. Bars: A, B = 2 cm; C–F = 5 μm.
