Amanita melleialba Zhu L. Yang, Qing Cai & Yang Y. Cui.
Index Fungorum number: IF551331; Facesoffungi number: FoF00898
Basidiomata small. Pileus 2.8–5 cm in diam., plano-convex to plane, center often slightly depressed, honey-coloured, yellowish (4A3–4) to yellow (3B5–6), becoming yellowish to whitish (3A2) toward margin, viscid when moist; margin tuberculate-striate (0.4–0.6R), non-appendiculate; volval remnants as subconical to granular, small warts up to 2 mm high, dirty white (5B2), cream-coloured to yellowish (4A2–3), randomly arranged, or densely placed at center; trama white (1A1), unchanging. Lamellae free, white (1A1), crowded; lamellar edges finely fimbriate, white (1A1), dirty white (5B2, 4B1–2) to cream-coloured (4A2–3); lamellulae truncate, plentiful, evenly distributed. Stipe 4–8×0.4–0.8 cm, subcylindric or slightly tapering upward, with apex slightly expanded, white (1A1) to cream-coloured (1A2), covered with white (1A1) floccose squamules above annulus, with white (1A1) floccose squamules to granules under annulus; context white, loosely stuffed to hollow in center; basal bulb subglobose to napiform, 0.8–1.2 cm in diam., white (1A1); volval remnants as white to cream-coloured (1A1) floccose squamules to granules, or forming a short limb. Annulus present, pendant from attachment 1.5–3 cm below apex of stipe, white (1A1) to cream-coloured (1A2), with a yellow floccose edge. Odor indistinct. (Fig.2)
Lamellar trama bilateral. Mediostratum 30–60 μm wide, composed of abundant ellipsoid inflated cells (35–60×16– 37 μm); filamentous hyphae abundant, 2–8 μm wide; vascular hyphae rare. Lateral stratum composed of abundant fusiform to ellipsoid inflated cells (22–65×9–20 μm), diverging at an angle of ca. 30–45° to the mediostratum; filamentous hyphae abundant, 2–6 (−9) μm wide; septa without clamps. Subhymenium 30–60 μm thick, with 2–3 layers of subglobose to ovoid or irregularly shaped cells, 9–17×7–15 μm. Basidia 30–50×9–14 μm, clavate, 4-spored; sterigemata 3–5 μm long; basal septa without clamps. Basidiospores [60/3/2] 7.5–9.5(−10) × (5.5–)6–7 μm [Q= (1.21–)1.29–1.58(−1.63), Qm=1.41±0.10], ellipsoid, sometimes broadly ellipsoid, inamyloid, colourless, hyaline, thin-walled, smooth; apiculus small. Lamellar edge appearing as sterile strip, composed of globose, subglobose to ellipsoid inflated cells (12–32×10– 25 μm), single and terminal or in terminal chains of 2–3, thin-walled, colourless, hyaline; filamentous hyphae abundant, 2–4 μm wide, irregularly arranged or ± running parallel to lamellar edge. Pileipellis 100–150 μm; upper layer (50– 70 μm thick) strongly gelatinized, composed of subradically to somewhat interwoven, thin-walled, colourless to nearly colourless, filamentous hyphae 3–5 μm wide; lower layer (50–80 μm thick) composed of radically and compactly arranged, filamentous hyphae 3–8 μm wide; vascular hyphae rare. Volval remnants on pileus composed of vertically to subvertically arranged elements; inflated cells very abundant to nearly dominant, globose to subglobose or ellipsoid to subfusiform (20–65×10–35 μm), in chains of 2–4, thin-walled, colourless to subcolourless; filamentous hyphae rare to fairly abundant, 3–6 μm wide, thin-walled, colourless to nearly colourless; vascular hyphae rare. Volval remnants on the stipe base composed of two layers of intergrading into each other. Outer layer composed of longitudinally to irregularly arranged elements: inflated cells abundant to very abundant, fusiform to ellipsoid, 20–45×10–30 μm, colourless to yellow brownish, thin- to slightly thick-walled, terminal or in chains of 2–3 and then terminal, becoming rare toward inner layer; filamentous hyphae very abundant to abundant; vascular hyphae rare. Inner layer somewhat gelatinized, filamentous hyphae very abundant to nearly dominant, mixed with scattered, long ellipsoid to clavate inflated cells, 65–150×15–20 μm. Stipe trama composed of longitudinally arranged, long clavate, terminal cells, 150–350×27–50 μm; filamentous hyphae scattered to fairly abundant, 2–9(−14) μm; vascular hyphae rare. Annulus slightly gelatinized, composed of subradially arranged elements; inflated cells very abundant, ellipsoid to long ellipsoid, 15–65×10– 28 μm, colourless, thin-walled, becoming elongated toward lower surface; filamentous hyphae abundant, 2– 5(−8) μm, colourless, thin-walled. Clamps absent in all parts of basidioma. (Fig. 3–4)
Habitat and distribution: Solitary or gregarious in subtropical forests dominated by Fagaceae. Known from southwestern and central China.
Material examined: CHINA, Hunan Province, Changsha City, Yuelu Mountain, Fagaceae (altitude ca. 260 m), 18 July 2014, S.C. Li 1 (HKAS 83216). Yunnan Province, Puer City, Caiyanghe Nature Reserve, Fagaceae (altitude 1300 m), 11 July 2014, G. Wu 1339 (HKAS 83446, holotype!); the same location, Fagaceae (altitude 1326 m), 11 July 2014, Xiao B. Liu 439 (HKAS 87085).
Notes: Amanita melleialba is characterized by its small basidiomata, ellipsoid basidiospores (7.5–9.5×6– 7 μm), volval remnants on the pileus dominantly composed of abundant inflated cells in chains of 2–4, and occurrence in subtropical forests dominated by plants of Fagaceae. Amanita melleialba is very similar to A. parvipantherina Zhu L. Yang, M. Weiss & Oberw., however, the latter possesses a brownish pileus with shorter marginal striations, larger basidiospores (8.5–11.5×6.5–8.5 μm) and is distributed in the mixed forests with Pinus yunnanensis. Our molecular phylogenetic analysis also suggested that A. melleialba is a separate species and is different from A. parvipantherina. Amanita melleialba may be confused with A. elata (Massee) Corner & Bas, a species originally described from Singapore. However, A. elata has volval remnants on the pileus as small, scattered, irregularly shaped, floccose-membranous, flat patches, which are easily washed off by rain, and globose to subglobose basidiospores.
Fig. 1 Phylogram of Amanita melleialba from Maximum likelihood (RAxML) analysis of LSU, rpb2 and tef1-α sequence data. Maximum likelihood bootstrap values greater than 50 % and Bayesian posterior probabilities over 0.90 are indicated above or below the nodes.