Amanita rimosa P. Zhang & Zhu L. Yang
Index Fungorm number:xxx; Face Fungorum number: xxx
Basidiomata small-sized. Pileus 50–62 mm wide, hemispheric when young, convex to applanate at maturity, dry, slightly subviscid, shiny when moist, minutely rimose around margin, pale yellow to cream (4A2-3) at center, white to yellowish white (3A1-2) towards margin. Margin non-striate, non appendiculate, context 2–3 mm thick above stem, soft, white (1A1) (Fig. 4a). Lamellae 4–5 mm broad, free, crowded, white to whitish (1A1). Lamellulae of 2–3 lengths, attenuate. Stipe 70–90 × 15–20 mm (length includes bulb), subcylindric, slightly tapering upwards, bulbous, covered with minute, white to whitish (1A1-2) squamules, turning slightly yellowish white when bruised. Context solid, white to whitish (1A1-2). Bulb globose to subglobose, marginate, 16–20 mm wide. Universal veil on stipe base as volval limb on bulb margin up to 10 mm high, white to whitish (1A1-2), limbus internus membranous, white (1A1). Partial veil subapical, membranous, thin, skirt-like, slightly striate, white (1A1). Odor not recorded.
Lamellar trama bilateral, divergent, mediostratum 35–40 μm wide, filamentous hyphae 3–5 μm wide, branching,hyaline, thin-walled, with terminal cells ellipsoid to fusiform, 30–75 × 10–28 μm thin-walled, vascular hyphae not observed. Subhymenium 25–32 μm thick, inflated cells in 2–3 layers, subglobose to ovoid, dominating, 15–25 × 10–20 μm. Basidia 38–42 × 15–18 μm, clavate, 4-spored, with sterigmata 4–6 μm long, clamps absent. Basidiospores (Fig. 4b–j) [50/2/2] (6.0–) 6.3–8.3 (−8.6) × (5.6−) 5.8–7.4 (−8.2) μm, (L’ = 7.0 μm, W’ = 6.6 μm, Q = 1.01−1.16 (−1.18), Q’ = 1.06 ± 0.05), smooth, hyaline, colorless, thin-walled, amyloid, globose to subglobose, occasionally broadly ellipsoid, often adaxially flattened, apiculus sublateral, small, cylindric to truncate-conic. Contents granular or rarely monoguttulate, white in deposit. Lamellar edge sterile, inflated cells dominating, subglobose to broadly ellipsoid, single or 2-3 in chain, 20–25 × 15–20 μm, hyaline, colorless, thin-walled. Pileipellis 130–190 μm thick, 2-layered. Upper layer 80–90 μm thick, filamentous hyphae 2–6 μm wide, slightly gelatinized, hyaline, colorless, thin-walled, with terminal cells ellipsoid to clavate to fusiform, 70–270 × 25–38 μm, lower layer 50–100 μm thick, filamentous hyphae 2–5 μm wide, non-gelatinized, hyaline or occasionally with intracellular pale yellow pigment, thin-walled. Universal veil on stipe base filamentous hyphae 2–4 μm wide, no inflated cells observed, gelatinized, branching, hyaline, thin-walled. Stipe trama longitudinally acrophysalidic. filamentous hyphae dominating, 1–5 μm wide. acrophysalides clavate, 120–310 × 25–45 μm, vascular hyphae rare. Partial veil filamentous hyphae 2–7 μm wide, branching, hyaline, colorless, thin-walled, inflated cells, clavate to ellipsoid, abundant, 20–45 × 10–35 μm, occasionally subglobose (12–25 × 10–20 μm), vascular hyphae rare.
Habitat: solitary or scattered on the ground in forest of Fagaceae.
Specimens examined: THAILAND, Chiang Mai Province, Mae-taeng District, Pha-daeng Temple, elev. 1,075 m, 09 June 2012, B. Thongbai, BZ201264 (MFLU 14-0064, BBH 40274), Chiang Rai Province, Chiang-khong District, Huay-sor Subdistrict, Nensomburn Village, 30 August 2014, B. Thongbai, BZ201386 (MFLU 15-0153, BBH 40581).
Distribution: China and Thailand.
Notes: Amanita rimosa is a member of Amanita [subgenus Lepidella] sect. Phalloideae. In the field, A. rimosa can be recognized by the pileus that is white to yellowish white towards the margin, the appearance of fine radial raised ridges on the pileus (lens sometimes required) and the minutely rimose pileus margin surface. The main microscopic characteristic is the slightly gelatinized upper layer of the pileipellis with abundant inflated hyphae, which is unique among species in sect. Phalloideae. The size of basidiomata, as well as size and shape of basidiospores of the Thai collections is very similar to the original description from China. The holotype and the Thai specimens were collected from evergreen broad-leaved forest with Fagaceae at elevations of 1,300 m and 1,075 m, respectively. The combined genes phylogenetic analyses indicated Thai A. rimosa sequences clustered with A. rimosa sequences from China. Amanita rimosa is a member of Amanita [subgenus Lepidella] sect. Phalloideae with 100% BS, PP = 1.0.