Amanita rubromarginata Har. Takah.
Index Fungorum number: IF 373370
Basidioma medium-sized to large. Pileus 6.0–10.0 cm diam., convex to plano-convex with the center depressed, reddish orange (7B7) over disk, or sometime orange red (8B7–8) at center and becoming light orange (5A4–5) towards the margin; universal veil on pileus absent; margin striate (0.4–0.5 R), non-appendiculate; context 4.5–8.0 mm wide, yellowish white (3A2), unchanging. Lamellae free, crowded, pale yellow to light yellow (4A3–4), with lamellar edges reddish orange (7B7–8); lamellulae truncate. Stipe 13.7–20.0 × 1.0–1.8 cm, subcylindrical with slightly tapering upwards, yellow (3A6–7), densely covered by reddish yellow to deep yellow (4A7–8) squamules; context broadly fistulose, yellowish white (3A2) to white (3A1). Bulb absent. Universal veil on stipe base saccate, membranous, up to 5 cm high, white (1A1). Partial veil subapical to apical, membranous, dark orange (5A7–8) to orange (6A6–7). Lamellar trama bilateral, divergent; mediostratum 20–25 μm wide, filamentous hyphae abundant, 2–11 μm wide; fusiform to ellipsoidal inflated cells 60–153 × 15–27 μm; vascular hyphae scarce. Subhymenium 25–30 μm thick in 1–3 layers, with subglobose to ellipsoidal or irregular cells, 8–18 × 5–13 μm. Basidia 32–46 × 8–13 μm, clavate, 4-spored with sterigmata 3–4 μm long; clamps present at base. Basidiospores 7.0–9.5 (–10.0) × 6.0–7.0 (–8.0) μm, Q = (1.08–) 1.13–1.50 μm, Qm = 1.28 ± 0.11, subglobose to broadly ellipsoid or ellipsoid, inamyloid, hyaline, thin-walled, smooth; apiculus small. Lamellar edge sterile; filamentous hyphae 3–7 μm wide, hyaline, thin-walled; inflated cells, with globose, pyriform to clavate, 15–46 × 12–27 μm, hyaline, thin-walled. Pileipellis 80–130 μm thick; 2-layered, upper layer 25–40 μm thick, filamentous hyphae 1–6 μm wide, gelatinized, branching, thin-walled, hyaline; lower layer 50–100 μm thick, filamentous hyphae 3–8 μm wide, branching, thin-walled, hyaline to light yellow; vascular hyphae rare. Inner part of universal veil on stipe base filamentous hyphae dominant 2–11 μm wide, hyaline to light yellow, thin-walled, branching; inflated cells, with subglobose, ovoid to clavate, 30–72 × 10–70 μm, hyaline, thin-walled; vascular hyphae rare. Outer surface of universal veil on stipe base similar to structure of inner part, but presenting more abundant inflated cells. Stipe trama longitudinally acrophysalidic; filamentous, undifferentiated hyphae 1–6 μm wide, thin-walled, frequently branching; acrophysalides 150–295 × 33–53 μm, thin-walled; vascular hyphae rare. Partial veil filamentous hyphae very abundant, 2–11 μm wide, hyaline, thin-walled; inflated cells scarce to locally abundant, ellipsoidal to clavate, 45–110 × 10–16 μm, hyaline to light yellow, thin-walled; vascular hyphae rare. Clamp connections present in all tissues of basidioma.
Habitat: Solitary to scattered on soil in tropical deciduous forests dominated by Dipterocarpus and Shorea.
Distribution: known from China, Japan, and Thailand, this study.
Specimens examined: Thailand, Chiang Mai Province, Mae Taeng District, 19°06′53.3″ N 98°44′22.7″ E, alt. 1718 m, 8 August 2019, Yuan S. Liu, STO-2019-451 (SDBR-CMUSTO-2019-451); STO-2019-452 (SDBR-CMUSTO-2019-452); Doi Saket District, 18°53′2″ N 99°9′17″ E, alt. 343 m, 2 August 2022, Kumla J. and Suwannarach N., CMUNK0854 (SDBR-CMUNK0854); Lumphun Province, Mae Tha District, 18°27′41″ N 99°10′30″ E, alt. 427 m, 25 July 2020, Kumla J. and Suwannarach N., CMUNK0780 (SDBR-CMUNK0780).
Remarks: Morphologically, A. rubroflava is easily confused with A. rubromarginata. However, A. rubroflava differs from A. rubromarginata by having a distinctly umbonate pileus and larger basidiospores (8.0–10.0 × 6.5–8.0 μm). Phylogenetically, Amanita javanica (Corner & Bas) Oda, Tanaka & Tsuda is closely related to A. rubromarginata. Meanwhile, both these two species share similar characteristics, such as an orange-red tone pileus and reddish yellow squamules covering their stipes. However, A. javanica has a distinctly umbonate pileus, while A. rubromarginata does not appear to display this characteristic.
Fig. 1 The phylogenetic tree derived from maximum likelihood analysis of 64 specimens of the combined ITS, nrLSU, rpb2, and tef-1 genes. The tree is rooted with A. retenta and A. shennongjiana. Numbers above branches are the bootstrap percentages (left) and Bayesian posterior probabilities (right). Bootstrap values ≥ 75% and Bayesian posterior probabilities ≥ 0.90 are shown. The scale bar displays the expected number of nucleotide substitutions per site. Sequences derived in this study are shown in red. Type species are shown in bold.