Agaricus guizhouensis Y. Gui, Zuo Y. Liu & K.D. Hyde
Index Fungorum number: IF 808758, MycoBank: MB808758
Pileus 5.2e12 cm in diameter, 0.5e0.8 cm thick, truncate-conical or convex to hemispherical, finally applanate; surface smooth, and white or covered with pastel yellow (oac814) to greenish-grey (oac816) appressed patches of irregular shape or triangular fibrillose squamules scattered over the entire white or pale yellow (oac815) background. Yellowishbrown patches or fibrillose squamules can be seen on the pileus of some young sporocarps, while they are easily removed by rain. Lamellae up to 0.4e0.6 cm broad, free, crowded, with intercalated lamellulae, white (oac909) to brown. Stipe 9e15.1 1e1.6 (1.7e2.1 at the base) cm, central, fistulose, clavate, tapering upward, bulbous, with copious rhizomorphs; surface white, smooth above the ring, fibrillose below the ring. Annulus superous, up to 0.9e1.2 cm broad, white, double, lower surface flocculose breaking in triangular scales arranged as a cogwheel, greenish-grey (oac816) or greyish-yellow (oac780) at the margin. Context white, turning yellowish-white (oac815) or yellow (oac855), then brownish-red (oac688) or pastel yellow (oac814), finally yellowish-green (oac891). Odour of bitter almonds at the base of the stipe and pileus surface after touching immature sporocarps, and slightly fungoid or bitter almonds in mature ones. Macrochemical reactions: KOH reaction positive vivid yellow (oac811) or yellowish-green (oac894) in young sporocarps. Schaffer’s reaction positive red (oac607) in young sporocarps. Microscopical characters: Basidiospores [446/9/4] (4.6–) 6–7(–10.9) (3–)3.7–4.1(–5.6) mm [avX = 6.6 – 0.3 3.9 – 0.1 mm, Q = (1.33–)1.50–1.91(–2.33), avQ = 1.68 – 0.1], elongate-ellipsoid, with a prominent oblique apiculus, attenuate at the apex without apical pore, smooth, thick-walled, brown. Basidia, (12–)14.4–24.6(–34.1) × 5.5–10(–10.9) mm, 4-spored, clavate with sterigmata 2 mm long on average; Cheilocystidia 3.6–16.6 × 3.2–14.3 mm (Q = 0.92–2.03), ellipsoid to subsphaerical or clavate, single or catenulate, smooth with intracellular diffuse brown pigment. Pleurocystidia absent. Pileipellis a cutis of hyphae 29–101.2 × 3.1–8.2 mm, thin, cylindrical, not constricted at septa, hyaline. Annulus composed of two types of hyphae, the first 39.5–78.6 × 3.8–8.6 mm, cylindrical, not constricted at septa, hyaline, the other 11.2–39.7 × 8.5–28.3 mm, cylindrical or slightly inflated, slightly constricted at septa, hyaline. (Figs 1–2)
Etymology: This taxon is so named because the collected specimens come mainly from Guizhou Province.
Holotype: HKAS 81081 (ITS Genbank: KJ755658)
Habitat: Gregarious on litter of pine needles and leaf, in mixed forests.
Specimen examined: CHINA: Guizhou Province, Longli County, Gujia Village, Guanying Mountain, soil covered with pine needles, and leaf litter, in mixed forests, N 26.495º, E 106.9º, altitude 1401.1 m, 13 Oct. 2012, GY-127800 (HKAS 81081). China: Guizhou Province, Longli County, Gujia Village, Xima Mountain, soil covered with pine needles and leaf litter, in mixed forests, N 26.491º, E 106.911º, altitude 1266.1 m, 13 Oct. 2012, GY-127700 (HKAS 81079); Ibid., Wudang County, Donglong Village, soil covered with pine needles and leaf litter, in mixed forests, N 26.784º, E 106.827º, altitude 1233.9 m, 6 Dec. 2012, GY-128986 (HKAS 81080); Ibid., N 26.783º, E 106.827º, altitude 1233.9 m, 6 Nov. 2012, GY-12110616 (HKAS 81085); Ibid., GY-1211184 (HKAS 81086). Ibid., Xiuwen County, Liuguang Village, Hexing, altitude 1189 m, N 26.978º, E 106.450º, 25 Oct. 2012, GY-1283998 (HKAS 81082); Ibid., E 106.434º, N 26.980º, altitude 1223 m, 17 Oct. 2012, GY-128053 (HKAS 81087); Ibid., E106.433º, N 26.972º, altitude 1210 m, 26 Oct. 2012, GY-12839910 (HKAS 81084); Yunnan Province, Kunming City, Kunming Institute of Botany, Chinese Academy of Sciences, 24 May 2008, T-288 (HKAS 54105).
Distribution: Known only from highland subtropical Southwest China
Notes. Agaricus guizhouensis is characterized by a white or a little yellowish or greyish pileus with yellowish squamules, the lower surface of the annulus breaking in scales arranged as a cogwheel, relatively small ellipsoid spores, and pyriform or subglobose, catenulate cheilocystidia with intracellular yellowish-brown pigments. It is commonly found in mixed forests dominated by pines and Fagaceae species in Guizhou Province, and was reported to be edible by some locals. The new species is macromorphologically similar to many species of section Arvenses having a white pileus. Agaricus guizhouensis is characterized by its scattered pastel yellow, greenish-grey or yellowish-brown patches or fibrillose squamules on the pileus, and pigmentation of the cheilocystidia which are usually hyaline or brownish-yellow in other species. However, a variation in the pigmentation of cheilocystidia in other species of section Arvenses (and also in other sections) have been also observed, for example in A. fissuratus and A. augustus, some collections also have cheilocystidia with abundant pigment. It is very difficult to distinguish A. guizhouensis from species with a similar or overlapping range of spore size such as A. abruptibulbus, A. greuteri or A. sylvicola. It cannot be excluded that specimens previously identified as A. sylvicola or A. abruptibulbus in China, could have been in fact A. guizhouensis.