Amanita ravicrocina Yuan S. Liu & S. Lumyong
Mycobank number: 842343
Basidioma small to medium-sized. Pileus 3.0–8.5 cm diam., convex to plano-convex, often slightly depressed at center, brown (5E5), greyish orange (5B4–5) to orange white (5A2), often darker at center and becoming paler towards margin; volval remnants on pileus often persistent as large, thick, white (1A1) patches slightly attached on pileus; margin striate (ca. 0.3–0.5), non-appendiculate; context white, unchanging. Lamellae free, crowded, white (1A1); lamellulae truncate. Stipe 5.6–13.1 cm long × 0.8–1.4 cm diam., slender, subcylindrical and slightly tapering upward, with apex slightly expanded, white (1A1), covered with white (1A1) fibrils, becoming floccose near basal bulb; context white (1A1), fistulose; basal bulb globose to subglobose, 1.8–2.9 cm diam., white (1A1); volval remnants on stipe base formed a collar-like or shortly limbate volva on limit between stipe and basal bulb, white (1A1). Annulus absent. Odor not recorded. Lamellar trama bilateral. Mediostratum 15–30 µm wide, composed of abundant clavate to cylindrical inflated cells (25–160 × 12–35 µm); filamentous hyphae abundant, 2–7 µm wide; vascular hyphae scarce. Lateral stratum composed of abundant ellipsoid to clavate inflated cells (50–155 × 7–18 µm), diverging at an angle of ca. 30 µm to 45 µm to mediostratum; filamentous hyphae abundant, 2–8 µm wide. Subhymenium 20–30 µm thick, with 2–3 layers of subglobose, pyriform, or irregular cells, 8–19 × 5–10 µm. Basidia 38–52 × 10–14 µm, clavate, four-spored; sterigmata 3–6 µm long; basal septa lacking clamps. Basidiospores [100/5/4] (7.0–) 8.0–9.5 (–10.5) × (6.0–) 7.0–8.5 (–9.0) µm, avl × avw = 8.7 × 7.5 µm, Q = (1.00–) 1.06–1.29 (–1.36) µm, Qm = 1.16 × 0.08, subglobose to broadly ellipsoid, inamyloid, colorless, thin-walled, smooth; apiculus small. Lamellar edge appearing as a sterile strip, composed of abundant subglobose to ellipsoid inflated cells (8–25 × 6–12 µm), single and terminal or in chains of 2–3, thin-walled, colorless; filamentous hyphae fairly abundant, 2–8 µm wide, irregularly arranged or parallel to lamellar edge. Pileipellis 60–100 µm thick, composed of radial, thin-walled, colorless, filamentous bhyphae 2–10 µm wide; vascular hyphae scarce. Volval remnants on pileus composed of irregularly arranged elements: filamentous hyphae abundant to very abundant, 2–10 µm wide, colorless, thin-walled, branching, anastomosing; inflated cells abundant, globose, subglobose, fusiform to ellipsoid, sometimes irregular, 20–90 × 14–46 µm, colorless, thin-walled, terminal or in chains of 2–4; vascular hyphae scarce. Volval remnants on stipe base is semblable with the structure of volval remnants on pileus, composed of irregularly arranged elements: filamentous hyphae very abundant to nearly dominant, 2–9 (–12) µm wide, colorless, thin-walled, branching, anastomosing; inflated cells fairly abundant to abundant, globose, subglobose, ellipsoid to clavate, sometimes irregular, 18–90 × 11–35 µm, colorless, thin-walled; vascular hyphae scarce. Stipe trama composed of longitudinally arranged, clavate terminal cells, 75–235 × 18–36 µm; filamentous hyphae abundant, 3–11 µm wide; vascular hyphae scarce. Clamps absent in all parts of basidioma.
Habitat: Solitary to scattered on soil in tropical deciduous forests dominant by Dipterocarpus and Shorea. Basidioma occurs in the rainy season during May to October.
Distribution: Currently known from northeastern Thailand.
Additional collections examined: Thailand, Kalasin Province: Kham Muang District, Na Bon, 16_530050 0 N, 103_410490 0 E, alt. 239 m, 12 August 2020, Yuan S. Liu, STO-2020-229 (SDBR-STO-2020-229); Yuan S. Liu, STO-2020-235 (SDBR-STO-2020-235); Sakon Nakhon Province: Phu Phan District, Khok Phu, 17_000090 0 N, 103_570340 0 E, alt. 291 m, 15 August 2020, Yuan S. Liu, STO-2020-283 (SDBR-STO-2020-283).
Notes: Amanita ravicrocina has a collar-like volva remnant on the limit between stipe and inflated basal bulb, which is not a common characteristic in A. section Amanita. Coupled with a brown tone pileus surface, A. ravicrocina could be easily singled out from other species in A. section Amanita, except A. ibotengutake T. Oda, C. Tanaka & Tsuda, A. pseudopantherina Zhu L. Yang ex Yang-Yang Cui, Qing Cai & Zhu L. Yang, and A. subglobosa Zhu L. Yang. Nevertheless, the latter three taxa are distinguished from A. ravicrocina by having the membranous annulus and pyramidal to subconical volva remnants on pileus. In addition, A. parvipantherina also possesses close likeness with A. ravicrocina. Both of them have small to medium-sized basidiomata and a light grey to brown pileus surface. However, A. parvipantherina has a white to brownish annulus, and its volva remnants on pileus are verrucose to pyramidal, while A. ravicrocina has a short annulus and appears as patchy volva remnants on pileus.
Fig 1. RAxML tree based on a combined of ITS + nrLSU + RPB2 + TEF1-a + TUB dataset. Bootstrap values (BS) for ML _ 50% and posterior probabilities (PP) for BI _ 0.95 are placed above or below the branches, respectively. Newly generated sequences are indicated in red and sequences from type material are marked with (T). The tree is rooted with Amanita yuaniana (HKAS58807 and HKAS68662) and A. caesareoides (HKAS92009 and HKAS92017).