Volvariella morozovae

Volvariella morozovae E.F. Malysheva & A.V. Alexandrova

Index Fungorum number: IF 821859

Basidiocarps medium-sized. Pileus 20–45 mm diam., at first convex to broadly campanulate, becoming plano-convex or plano-umbonate with low broad umbo, with even or slightly serrulate non-striate margin fringed with fluffy fibrils; non-hygrophanous; surface not viscid; sandy brown, cinereous, brownish grey or ash brown, darker at centre—greybrown, dirty brown or blackish, towards margin paler to beige or whitish; radially silky fibrillose to hairy with some short ascending hairs. Lamellae rather crowded to fairly distant, free, with lamellulae, slightly ventricose, initially whitish then pink to brownish pink, with concolorous even edge. Stipe 35–50 × 3–4 mm, cylindrical, not or somewhat broadening towards base (up to 6–7 mm), solid, white or with light ochraceous or buff shades; entirely minutely pubescent to hairy. Volva thin, rather cartilaginous, saccate, dirty grey-brown to olivaceous-brown with rusty brown spots, irregularly lobed, with felted to woolly outer surface. Context white. Smell and taste indistinct. (Fig. 2)

Basidiospores [90, 3, 3] 5–6.5 × 3.5–4.5 μm (Lav = 5.7 μm, Wav = 4.0 μm, Q = 1.23–1.65, Q* = 1.46), broadly ellipsoid, oblong to lacrymoid, some rather ovoid, hyaline in KOH, thick-walled. Basidia 13.5–20 × 7–8.5 μm, 4-spored, broadly clavate with a medial constriction at maturity. Cheilocystidia 20–55 × (8)10–18 μm, numerous, extremely variable in size and shape, mainly ventricose-lageniform, broadly fusiform, some proportion utriform or clavate, sometimes with subglobose or furcated apex, thin- or slightly thick-walled, hyaline in 3% KOH. Pleurocystidia 42–57 × 18–30 μm, rare or scarce, utriform or broadly clavate, slightly thick-walled, hyaline in 3% KOH. Lamella trama composed of hyaline hyphae 4–10 μm wide, thin-walled. Pileipellis a cutis, made up of short-celled, slightly thickwalled, non-gelatinous hyphae, 20–35 μm wide, with intracellular grey-brown pigment; transforming into a trichoderm at centre of pileus, with ascending cylindrical, fusiform or sublageniform terminal elements usually more than 100 μm long. Stipitipellis a cutis, composed of long, cylindrical, hyaline hyphae, 10–12 μm wide; hairs cylindrical, hyaline, thin-walled, 150–200 μm long and 6 μm wide. Clamp connections absent in all tissues examined. (Fig. 3)

Habitat and known distribution: Solitary, on wood or litter in tropical montane polydominant constantly moist forests. So far only known from several sites in Kon Ka Kinh National Park (Vietnam).

Specimens examined: VIETNAM, Gia Lai Province: Mang Yang districts, A Yun commune, A Yun village, Kon Ka Kinh National Park, tropical montane polydominant constantly moist forest dominated by trees of Euphorbiaceae, Myrtaceae, Moraceae, Duabangaceae, Lauraceae, Fagaceae and Meliaceae, path along the river, N 14.21977°, E 108.31944°, on wood of unknown tree, 14 May 2016, O. Morozova 313229 (holotype LE!; GenBank MF377507 - ITS, MF377508 - LSU, MK940800 - tef1); Central Highlands region (Tây Nguyên), Kon Tum Plateau, Gia Lai Province, K’Bang districts, Kroong (K’Rong) commune, K’Rong village, Kon Ka Kinh National Park, tropical montane polydominant forest dominated by trees of Myrtaceae, Meliaceae, Anacardiaceae, Fagaceae and Theaceae, on a mountain slope, N 14.305722°, E 108.443513°, on litter, 13 May 2017, A. Alexandrova 313322 (LE!; GenBank MK882994 - ITS, MK940801 - tef1); the same territory, wide crest of the ridge, tropical montane polydominant constantly moist forest dominated by trees of Euphorbiaceae, Myrtaceae, Moraceae, Duabangaceae, Lauraceae, Fagaceae and Meliaceae, N 14.297821°, E 108.425317°, on dead wood, 16 May 2017, A. Alexandrova 313323 (LE!; GenBank MK882995 - ITS, MK940802 - tef1).

Notes: Volvariella morozovae is characterized by medium-sized basidiocarps with brownish grey and hairy pileus, olivaceous-brown or rusty brown felted volva, small (5–6.5 × 3.5–4.5 μm) elongate-ellipsoid to lacrymoid basidiospores. There are several well-known or poorly known species with small or medium-sized basidiocarps, grey or brown pileus and coloured volva, similar to V. morozovae. Among them Volvariella cinerascens (Bresàdola 1929: 532) M.M. Moser (1953: 109), V. fuscidula (Bresàdola 1905: 159) M.M. Moser (1953: 110), V. murinella (Quélet 1883: 391) M.M. Moser in Dennis, P.D. Orton & Hora (1960: 167), V. taylorii (Berkeley & Broome 1957: 398) Singer (1949: 401), V. lepiotospora Singer (1955: 774), and V. nigrodisca Shaffer (1962: 567). This is a rather intricate group of fungi in terms of difficulties in distinguishing them from each other, yet the studied Vietnamese collections do not agree in all respect with the description of any of these species: Volvariella cinerascens is European species, differing in a glabrous surface of the pileus with distinctly striate margin and narrow basidiospores (3–3.5 μm) (Moser 1967). Volvariella fuscidula has originally viscid pileus with striated margin, the blackening stipe and larger (6.7–8.2 × 4.7–5.5 μm) basidiospores (Shaffer 1962). Volvariella murinella, distributed in temperate regions of Europe, is quite similar to V. morozovae in basidiocarp appearance, spore shape and size, but differs in larger (40–100 × 10–50 μm) cheilo- and pleurocystidia of another shape, as well as prevalence of short elements in pileipellis structure (Boekhout 1990). Volvariella taylorii, widely distributed in Europe and North and South America, mostly differs in its shiny and often subviscid pileus, larger basidiospores (5.5–8.7 × 4–6 μm), larger and differently shaped hymenial cystidia (Shaffer 1957, Boekhout 1990). Volvariella lepiotospora is characterized, unlike V. morozovae, by dark brown to black colour of pileus, arachnoid volva, narrower (3–3.7 μm) basidiospores, presence of clamps and clavate cheilocystidia (Shaffer 1957). Volvariella nigrodisca, North American species, differs from V. morozovae in its blackish pileus with striate margin, slightly longer basidiospores (5.7–7.3 μm) and obovoid or clavate cheilocystidia (Shaffer 1962). Volvariella leucocalix Sá & Wartchow (2016: 364), recently described from Brazil, also actually seems to resemble V. morozovae in macroscopic characters but differs from the latter in smaller basidiospores (5–5.6 × 2.6–3.6 μm), shape of cheilo- and pleurocystidia, and white smooth volva. The result of Blast search of GenBank database using the nrITS (625 bp) sequence of V. morozovae holotype showed Volvariella sp. from Pakistan (GenBank KY636377) and from India (GenBank KR349630), and V. nullicystidiata from Brazil (GenBank EU920671) as the closest hits, but with extremely low indexes of identity: with 89%, 87%, and 84% respectively. The nrITS and nrLSU sequences of V. morozovae form a distinct well-supported clade on the phylogenetic tree (Fig. 1) confirming the independent taxonomic status of the species.

Fig. 1 Best tree from the ML analysis of the nrITS-nrLSU data set for Volvariella with Cantharocybe gruberi as outgroup. Bootstrap support values and Posterior probability (BS/PP) are given above the branches. All tips are labelled with taxon name and voucher ID. For taxa in bold the sequences are generated in present study.

Fig. 2 Mature basidiocarps of Volvariella morozovae. A. LE 313229 (holotype, photo by O. Morozova). B. LE 313322 (photo by A. Alexandrova). C–D. LE 313323 (photo by A. Alexandrova). Scale bars = 1 cm.