Panaeolus nigrescens M. Q. He & R. L. Zhao, sp. nov.

Panaeolus nigrescens M. Q. He & R. L. Zhao sp. nov. Fig. 10 Etymology. nigrescens (Lat.) refers to the black, grayish-black color of the pileus. Diagnosis. Panaeolus nigrescens has small, gray basidiomes with black hygrophanous stripes on the pileus and ellipsoid basidiospores. Holotype. CHINA. Gansu Province: Zhangye, 17 August 2018, Zhi-Ling Lin, HMAS 287499 (ZRL 20180732) Description. Pileus 6.9–28.8 mm in diam., conic, occasionally campanulate when getting mature, disc slightly umbonate or rarely flattened, background gray (pantone 421 c), disc black, hygrophanous stripes black (pantone 426 c), mottled and radially streaked, surface dry, margin slightly crenate. Lamellae adnate, close, broad, mottled grayish, entire, with a white edge. Stipe equal, flexuous, hollow, 52.6–126.7 mm long, 1.8–4.1 mm thick, white, pruinose, longitudinally striate, base with whitish mycelium, getting brown when touched, cut, or bruised. Basidiospores 10.7–14.0 × 6.5–8.7 μm, [x = 12.0 ± 0.7 × 7.6 ± 0.5, Q = 1.5–1.8, Q m = 1.6 ± 0.1, n = 20], ellipsoid, blackish brown when mature, smooth, thick wall, germ pore distinctive. Basidia 19.6–26.0 × 8.8–11.1 μm, 4 - spored, smooth, hyaline. Cheilocystidia 26.2–46.4 × 3.3–8.8 μm, narrowly cylindrical or flexuose, with a slightly inflated base, hyaline, smooth. Pleurocystidia absent. Cuticle composed of large vesicles, pileocystidia 12.9–46.9 × 9.4–35.5 μm, spheropedunculate, hyaline. Caulocystidia 12.1–47.3 × 5.0–10.1 μm, cylindrical or narrowly clavate, flexuose, or narrowly obovoid, hyaline, smooth. Habitat. Grows on pastures and soil. Psilocybin-producing. Nonproducing (ZRL 20180732, see Suppl. material 1: fig. S 10). Notes. Panaeolus nigrescens is a distinctive species in subclade A 1, characterized by its black or grayish black basidiomes, a pruinose stipe with longitudinal striations, and ellipsoid basidiospores. Compared with closely related species, namely P. limoniformisporus, P. medogensis, and P. pallidus, P. limoniformisporus most closely resembles P. nigrescens in the field. However, under the microscope, the two species can be separated by differences in basidiospore shape, with P. nigrescens having ellipsoid basidiospores and P. limoniformisporus having limoniform basidiospores. Specimens examined. China. Gansu Province: Zhangye, Qilian Mountain National Nature Reserve, Kangle Grassland, 38.384457°N, 100.653658°E, alt. 2800 m, 30 August 2016, Rui-Lin Zhao, Jean-Marc Moncalvo, ZRL 20161807, ZRL 20161828, ZRL 20161875; Haichaoba Forestry Park, 26 August 2018, Ming-Zhe Zhang, ZRL 20181924.