Agaricales » Amanitaceae » Amanita

Amanita cf. rubromarginata

Amanita cf. rubromarginata Har. Takah.

Index Fungorum number:xxx; Face fungorum number:xxx

Basidiomata small to medium-sized. Pileus 60–75 mm wide, hemispherical when young then convex to plano-convex to applanate at maturity, dry, subviscid when moist, with pale, short projecting hairs at center, carrot red to deep orange (6B7-8) to brownish orange (6C8) at center, grayish orange or apricot (5B5-6) toward margin. Margin non-appendiculate, with marked long sulcate striations on outer half of pileus. Context 3–7 mm thick above stem, yellowish white (2A2). Lamellae 5–10 mm broad, free, crowded, subventricose, yellowish (3A2) with margin markedly darker, red to reddish orange (7B7-8), fimbriate, lamellulae of 3–4 lengths, truncate. Stipe 50–110 × 4–14 mm, subcylindrical, slightly tapering upwards, yellowish white (3B2), above partial veil covered with minute reddish orange (7B7-8) fibrils or squamules forming irregular transverse zones. Context broadly fistulose to slightly chambered, yellowish white (3A2). Universal veil on stipe base as saccate volva, sheathing, up to 25 mm high, sticky, robust, thick, white (1A1). Partial veil subapical, membranous, pendant, large, thick, margin striate, reddish orange (7B7-8). Odor not recorded. Lamellar trama bilateral, divergent, mediostratum 35–40 μm wide, filamentous hyphae 2–5 μm wide, branching, hyaline, thin-walled, with terminus clavate to subfusiform, 90–120 × 25–30 μm, vascular hyphae rare. Subhymenium 30–40 μm thick, 2-3 layers of subglobose to ellipsoid cells, 15–20 × 10–15 μm. Basidia 25–30 × 10–15 μm, clavate to pyriform, 4-spored, with sterigmata 4–6 μm long, clamps present at base. Basidiospores  [50/2/2] (7.0–) 7.4–9.9 (–10.2) × (5.4–) 5.6–7.0 (–7.7) μm, (L’ = 8.8 μm, W’ = 6.3 μm, Q = (1.15–) 1.30–1.60 (–1.66), Q’ = 1.41±0.10), smooth, hyaline, colorless, thin-walled, inamyloid, ellipsoid, rarely broadly ellipsoid and elongate, adaxially flattened, apiculus rather variable, sublateral, very prominent to rather small, cylindric to truncateconic. Contents mostly monoguttulate, occasionally granular, white in deposit. Lamellar edge sterile, filamentous hyphae 2–7 μm wide, with inflated elements, colorless or occasionally with intracellular pale brown pigment, thin walled, subglobose to globose cells dominating, 22–25 × 18–20 μm, colorless, or occasionally with intracellular pale brown pigment, thin-walled. Pileipellis 70–100 μm thick, 2-layered, upper layer 30–50 μm thick, filamentous hyphae 3–8 μm wide, strongly gelatinized, hyaline, branching, thin-walled, lower layer 40–50 μm thick, filamentous hyphae 7–14 μm wide, non-gelatinized, branching, hyaline or occasionally with intracellular yellowish pigment, thin-walled. Universal veil on stipe base filamentous hyphae 5–8 μm wide, branching, hyaline or occasionally with intracellular yellow pigment, thin-walled, ellipsoidal to subglobose cells 20–28 × 18–26 μm, hyaline or occasionally with intracellular yellow pigment, thin-walled. Stipe trama longitudinally acrophysalidic, filamentous hyphae 2–6 μm wide, branching, hyaline, thin-walled, acrophysalides not described. Partial veil filamentous hyphae 2–8.5 μm wide, hyaline, occasionally with intracellular yellow pigment, thin-walled, with terminal clavate to ellipsoid cells, 27–65 × 16–52 μm.

Habitat: solitary or scattered on ground in forest of Fagaceae.

Specimens examined: THAILAND, Chiang Mai Province, Mae-on District, near Chiang Mai/ Lampang border, elev. 1,517 m, 02 July 2014, B. Thongbai, BZ201423 (MFLU 15-01418, BBH 40585), Lampang Province, Meuangpan District, elev. 1,170 m, 03 July 2014, B. Thongbai, BZ201425 (MFLU15-01420, BBH 40586).

distribution: southwestern Japan and now Thailand.

Notes: Amanita rubromarginata is a member of Amanita sect. Caesareae falling in the ‘jacksonii’ clade of Sánchez-Ramírez et al.. In the field, the distinguishing morphological characteristics of A. rubromarginata include distinctive long-sulcate striations on the margin of the pileus, glabrous to subviscid surface texture when moist, carrot red to deep orange to brownish orange, grayish orange or apricot colors toward the margin, long and thick reddish orange partial veil and white saccate volva. The distinctly reddish-orange, fimbriate margin of the lamellae is unique among those similar species with an orange to brownish orange to reddish pileus, e.g., A. hemibapha var. hemibapha (Berk. & Broome) Sacc. var. hemibapha, A. hemibapha var. ochracea Zhu L.Yang, and A. javanica (Corner & Bas) T. Oda, C. Tanaka & Tsuda as well as ll known spcies in the Americas and Europe. We are hesitant to firmly assign these collections to A. rubromarginata at this time because according to illustrations in the recent book of SW Japanese fungi (Terashima et al. 2016), as the mushroom ages, the center of the cap can become nearly black; and the margin, olive. We did not observe these characteristics in either of the Thai collections. The size of basidiomata as well as the size and shape of basidiospores of the Thai collections is similar to dimensions given in the original description from Japan (Takahashi 2004). The holotype was collected in an evergreen, broad-leaved forest with Quercus miyagii Koidz. and Castanopsis cuspidata (Thunb. ex Murray) Schottky var. sieboldii (Makino) Nakai. No elevation was recorded. The Thai specimens were collected at elevations of 1,170–1,517 m in fagaceous forest with Castanopsis spp.