Volvariella neovolvacea J. Kumla, N. Suwannarach and S. Lumyong.
Pileus 65–80 mm in diameter, convex, umbo and slightly inflexed margin, brownish orange (5C3) to greyish brown (6E3–7E3), non-hygrophanous, with fibrillose to appressed squamulose surface; margin decurved to straight, thin, crenulate; context soft, white (4A1) to light yellow (4A5). Lamellae free, ventricose, close, moderately thin, soft, orange white (6A2) turning pinkish white (7A2) with age; edge finely fimbriate, concolorous with faces; lamellulae present, very variable in length, mostly in one tier. Stipe 85–110 × 20–25 mm, central, tapered from the base to apex, solid, grey (6B1), entirely pubescent; context white (4A1) to light yellow (4A5); annulus absent. Volva 30–50 mm high, thick, mostly free, saccate, fragile, white (6A1) to greyish brown (6E3). Spore print pinkish (7A2). Basidiospores (6.5)6.7–7–7.5(8) × (5)5.2–5.5–6(7) µm (n = 50), Q= 1.14–1.45, Q = 1.28 ± 0.1, broadly ellipsoid to ellipsoid, thick-walled, hyaline, inamyloid. Basidia 27–40 × 7.5–11 µm, narrowly to broadly clavate, hyaline, 4-spored; sterigmata up to 2.5 µm long. Pleurocystidia 45–98 × 23–77 µm, clavate to broadly lageniform, thin-walled, hyaline. Cheilocystidia 29–57 × 9–22 µm, clavate to broadly lageniform, thin-walled, hyaline. Hymenophoral trama inverse, made up of thin-walled hyaline hyphae, 5–20 µm wide. Pileipellis a cutis, with terminal elements 37–98 × 8–16 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 22–60 × 8–15 µm, cylindrical, sometimes with a narrowed or slightly strangulated apex, colorless or with pale brown intracellular pigment. Clamp connections absent in all tissue types.
Ecology and distribution: Fruiting solitary or gregarious on soil in grassland. Known only from northern Thailand.
Additional specimens examined: THAILAND, Chiang Mai province, Chiang Mai University campus, on soil in grassland, July 2020, N. Suwannarach and J. Kumla, SDBR-CMUNK0760, gene sequences OM417505 (ITS) and OM417507 (nrLSU).
Note: Morphologically, the size of the pileus (65–80 mm in diameter) in V. neovolvacea was clearly larger than those of the brownish-orange to greyish brown Volvariella species, namely V. aethiops (30–50 mm in diameter), V. caesiotincta (44 mm in diameter), V. morozovae (30–40 mm in diameter), V. murinella (30–60 mm in diameter), V. pseudovolvacea (30–60 mm in diameter), V. thailandensis (35–60 mm in diameter), and V. taylorii (20–50 mm in diameter). In addition, V. bakeri, distributed only in the USA, has a larger pileus size (100 mm in diameter) than V. neovolvacea. However, the basidiomata size of V. neovolvacea was similar to V. pulla, V. rostricystidiata, V. terastia, and V. volvacea. The smaller size of the basidiospores in V. rostricystidiata and V. terastia clearly distinguishes them from V. neovolvacea. Additionally, the basidiospores of V. neovolvacea (6.5–8.0 × 5.0–7.0 µm, Q = 1.28) were wider than V. volvacea (6.0–9.0 × 4.7–5.7 µm, Q = 1.42). The wider size of pleurocystidia in V. neovolvacea clearly differed from V. pseudovolvacea, V. pulla, V. rostricystidiata, and V. terastia. Our phylogenetic results from the combined ITS and nrLSU sequences confirmed that V. neovolvacea formed a monophyletic clade, which clearly separated it from the other morphologically related Volvariella species. The phylogenetic analysis also supports the determination that V. neovolvacea and V. volvacea are different species. Volvariella neovolvacea forms a sister taxon to V. sathei. However, the white to yellowish-white pileus of V. sathei clearly separates it from V. neovolvacea. The ITS sequence of V. neovolvacea is 95.64% and 94.00% similar to V. sathei (JN792550) and V. cf. sathei (KF926663), respectively.
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.