Volvariella thailandensis N. Suwannarach, J. Kumla, and S. Lumyong
Pileus 35–50 mm in diameter, convex to plano-convex with a low broad umbo, greyish brown (6E3–7E3) with slightly darker color at the center, non-hygrophanous, with fibrillose to appressed squamulose surface; margin decurved to straight, thin, crenulate; context soft, light yellow (4A5). Lamellae free, ventricose, close, moderately thin, soft, pale orange (6A3) turning brownish orange (6C6) with age; edge finely fimbriate, concolorous with faces; lamellulae present, very variable in length, mostly in one tier. Stipe 40–65 × 4–5 mm, central, tapered from the base to apex, solid, greyish brown (6E3) to dark brown (6F5), slightly paler near the base, entirely pubescent; context light yellow (4A5); annulus absent. Volva 15–18 mm high, thick, mostly free, saccate, fragile, white (6A1) to greyish brown (6D4). Spore print pinkish (7A2). Basidiospores (5.5)6–7–6.5(7) × (4)4.4–5–5.5(6) µm (n = 50), Q = 1.16–1.50, Q = 1.30 ± 0.1, subglobose to broadly ellipsoid, thick-walled, hyaline, inamyloid. Basidia 15–35 × 6–8 µm, narrowly to broadly clavate, hyaline, four-spored; sterigmata up to 3 µm long. Pleurocystidia 35–77 × 17–30 µm, broadly fusiform to lageniform, thin-walled, hyaline. Cheilocystidia 32–48 × 6–10 µm, narrowly to broadly clavate, broadly lageniform, thin-walled, hyaline. Hymenophoral trama inverse, made up of thin-walled hyaline hyphae, 3–10 µm wide. Pileipellis a cutis, with terminal elements 65–150 × 4–16 µm, variable in size, narrowly clavate to clavate, sometimes with a narrowed or slightly strangulated apex, colorless or with pale brown intracellular pigment. Stipitipellis a cutis, terminal elements 35–80 × 6–9 µm, cylindrical, sometimes with a narrowed or slightly strangulated apex, colorless or with pale brown intracellular pigment. Clamp connections absent in all tissue types.
Additional specimens examined: THAILAND, Chiang Mai province, Chiang Mai University campus, on soil in grassland, August 2020, J. Kumla and N. Suwannarach, SDBR-CMUNK0958, gene sequences OM417510 (ITS) and OM386669 (nrLSU).
Note: Based on the morphology, the brownish-orange to greyish brown pileus and size of V. thailandensis were similar to that of V. aethiops, V. caesiotincta, V. morozovae, V. murinella, V. pseudovolvacea, V. rava, and V. taylorii. However, the larger size of the basidiospores and basidia in V. thailandensis differs from V. pseudovolvacea. The longer and shorter sizes of basidiospores in V. thailandensis clearly distinguishes it from V. murinella and V. aethiops, respectively. Additionally, the pleurocystidia (35–77 × 17–30 µm) of V. thailandensis were found to be wider than of the V. taylorii (35–49 × 8–10 µm) found in Europe, South Korea, the USA, and Vietnam. The wider cheilocystidia in V. caesiotincta (34–65 × 9.6–19 µm), V. morozovae (40–50 × 13–18 µm), V. pulla (24–87 × 9–17 µm), V. rava (55–80 × 15–25 µm), and V. taylorii (28–43 × 9–13 µm) clearly distinguishes them fromV. thailandensis (32–48 × 6–10 µm). The phylogenetic analyses of the combined ITS and nrLSU sequences confirmed that V. thailandensis formed a monophyletic clade, which clearly separated it from the other Volvariella species. Volvariella thailandensis is closely related to V. neovolvacea and V. sathei. However, it is morphologically quite different from V. sathei which has white to yellowish white pileus. Moreover, V. thailandensis is characterized by smaller basidiomata and wider cheilocystidia than V. neovolvacea.
Fig 1. Phylogram derived from maximum likelihood analysis of 50 specimens of the combined ITS and nrLSU genes. Cantharocybe virosa and Cuphophyllus yacurensis were used as the outgroup. The numbers above branches represent bootstrap percentages (left) and Bayesian posterior probabilities (right). Bootstrap values ≥75% and Bayesian posterior probabilities ≥0.90 are shown. The scale bar represents the expected number of nucleotide substitutions per site. Sequences obtained from this study are in red. Type species are in bold.