Agaricus longistipes Y. Gui, Zuo Y. Liu, Callac, L.A. Parra & K.D. Hyde.
Index Fungorum number: IF 808757, MycoBank: MB808757
Pileus 4–8 cm in diameter, up to 0.5 cm thick, globose to ovoid when young, then usually hemispherical, finally plano-convex; surface smooth, white, near the margin with floccose to fibrillose scales, exhibiting a yellowish-white (oac683) tone at the disc when mature; surface colour turns lively red after rain. Lamellae up to 0.55 cm broad, free, crowded, with intercalated lamellulae, whitish to pink or grayish pink, later grayishbrown, finally dark brown. Stipe 8.5–11.6 × 0.6–0.8 (0.7–1.1 at base) cm, cylindrical, slightly tapering upwards with abundant rhizomorphs at the base; surface smooth above the annulus, conspicuously flocculose to fibrillose below the annulus, white. Annulus superous, about 1–1.5 cm broad, double, upper surface smooth, lower surface floccose, white. Context, white (oac909), discolouring from yellowish grey (oac732) to brownish-orange (oac717) at the base of stipe. Odour like bitter almonds on the pileus and at the base of stipe when bruised. Macrochemical reactions: KOH reaction positive deep yellow; Sch€affer’s reaction positive orange. Microscopical characters: Basidiospores [93/4/2] (6.7–) 7.7–8.8(–10.7) × (4–)4.6–5(–5.6) mm [avX = 8.2 ± 0.3 × 4.9 ± 0.1, Q = (1.43–)1.60–1.89(–2.25), avQ = 1.75 – 0.07], elongate-ellipsoid, with a prominent oblique apiculus, attenuate at the apex, without apical pore, smooth, thick-walled, brown. Basidia 18.7–26.5 (–27.5) × 7.4–11.1 mm, 3 or 4- spored, clavate, with sterigmata 1.7 mm on average. Cheilocystidia 8.2–29.9 × 7.3–18.2 mm (Q = 0.89–2.38), pyriform or subglobose, simple or catenulate with intracellular granulose brownish-yellow pigment. Pleurocystidia absent. Pileipellis made of two types of hyphae, the first 68.1–146 × 4.1–8.5 mm in diameter, thin, cylindrical, hyaline, not constricted at septa and the other 35.8–117.4 × 15.2–39.4 mm in diameter, cylindrical, agglutinated, hyaline, slightly constricted at septa. Annulus hyphae, 16.8–67.7 × 3.2–19.6 mm in diameter, ellipsoid or cylindrical, smooth, hyaline, not constricted or rarely slightly constricted at septa. Stipitipellis (below the annulus) a cutis of hyphae (5–)24–50.6 × 4.1–13.7 mm in diameter, cylindrical to slightly inflated, smooth, and hyaline. (Figs 1–2)
Etymology: Referred to the long and slim stipe.
Holotype: HKAS 81066 (ITS Genbank: KJ755643)
Habitat Gregarious in soil covered with pine needles and leaf litter, in mixed forests.
Specimen examined: CHINA Guizhou Province, Longli County, Gujia Village, Xima Mountain, N 26.497º, E 106.906º, 1439.7 m, 7 Aug. 2012, GY-124427 (HKAS 81066). Distribution: Known only from highland subtropical Southwest China. China: Guizhou Province, Longli County, Gujia Village, Guanying Mountain, N 26.482º, E 106.856º, 1430.2 m, 7 Aug. 2012, GY-124459 (HKAS 81067).