Volvariella niveosulcata E.F. Malysheva, O.V. Morozova & A.V. Alexandrova
Index Fungorum number: IF 831057; MycoBank number: MB 831057
Basidiocarps small. Pileus 7–15 mm diam., at first convex, becoming applanate or plano-convex with low broad umbo, with undulating, slightly serrulate, sulcate, very thin and translucent margin; non-hygrophanous; surface not viscid; white, creamy, darker at centre—sandy or pale beige, towards margin with pinkish tint apparent from the pink lamellae beneath; radially silky fibrillose. Lamellae distant, free, with solitary lamellulae, ventricose, salmon coloured, with concolorous even edge. Stipe 20–35 × 1–2 mm, cylindrical, equal, solid, cartilaginous, shiny, white; smooth at upper part but pruinose to minutely squamose at lower part. Volva thin, cottony, saccate, pure white, irregularly lobed, with felted outer surface. Context white. Smell and taste indistinct. (Fig. 2)
Basidiospores [30, 1, 1] (6.5)7–9 × (5)5.5–6.5 μm (Lav = 8.0 μm, Wav = 5.9 μm, Q = 1.19–1.58, Q* = 1.37), broadly ellipsoid, ellipsoid, some ovoid, hyaline in KOH, thick-walled. Basidia 23–30 × 8–13 μm, (2-,3-)4-spored, narrowly to broadly clavate with a prominent medial constriction. Cheilocystidia 46–75 × 16–30 μm, rather numerous, narrowly to broadly clavate or utriform, thin-walled, hyaline in 3% KOH. Pleurocystidia rare or scarce, similar to cheilocystidia in shape and size. Lamella trama composed of hyaline hyphae 3–6 μm wide, thin-walled. Pileipellis a cutis, composed of slightly thick-walled, non-gelatinous, hyaline or yellowish hyphae, 10–15 μm wide. Stipitipellis a cutis, compose of long, cylindrical, hyaline in 3% KOH hyphae, 8–16 μm wide, some slightly incrusted. Clamp connections absent in all tissues examined. (Fig. 3)
Habitat and known distribution: In small group, on soil among grass. So far only known from the type locality.
Specimen examined: Holotype.
Notes: Volvariella niveosulcata is distinguished by tiny basidiocarps with white or creamy pileus, pure white stipe and volva, and medium-sized basidiospores (Lav = 8.0 μm, Wav = 5.9 μm). Volvariella pusilla (Persoon 1799: 36) Singer (1949: 401) and V. pusilla var. minuta K. Acharya, A.K. Dutta & P. Pradhan (2012: 936), which also produce suchlike tiny and white basidiocarps, are macroscopically most similar to the new species, but they differ in microscopical characters. The type variety of V. pusilla has smaller basidiospores (av. 5.5–7(7.8) × 4–5.5 μm) and differently shaped hymenial cystidia (usually fusiform with branched apex or lageniform) (Shaffer 1957, Boekhout 1990). Volvariella pusilla var. minuta is characterized and distinguished by bilobed volva, smaller basidiospores av. 6.9–7.1 × 4.7–5.5 μm, much smaller sized (27–28.5 × 7–10.5 μm) and also differently shaped (cylindrical or clavate) cheilo- and pleurocystidia (Acharya et al. 2012). The North American Volvariella pellucida Shaffer (1962: 570) though closely resembles Volvariella niveosulcata, differs by its vinaceous buff volva and fusoid-ventricose or lageniform cheilo- and pleurocystidia (Shaffer 1962). Volvariella smithii Shaffer (1957: 568) has slightly larger basidiocarps with smooth polished pileus, coloured volva and smaller (4.7–7 × 3.1–3.9 μm) ovoid basidiospores (Shaffer 1957). Volvariella hypopithys (Fries 1874: 183) M.M. Moser (1953: 110) has larger basidiocarps with squamulose, 20–65 mm broad pileus, and pubescent stipe 30–60 mm long, coloured volva and narrower (3.5–5 μm) basidiospores (Boekhout 1990). Two other species, Volvariella delicatula (Massee 1912: 254) Manjula (1983: 92) and V. liliputiana (Hennings 1901: 333) G.C. Rath (1963: 527), originally described from India, also similar in having small white basidiocarps, but the former differs from the new species by its fimbriate volva and subglobose basidiospores (Massee 1912), and the latter in its velvety pileus, shorter stipe (up to 15 mm) and subglobose basidiospores (Hennings 1901). The phylogenetic analyses show that the new species is clustered in one group together with V. guttulosa, another species described from Vietnam (Fig. 1) but both taxa differ completely from each other based on nrLSU sequences (more than 10% dissimilarity). Further, they differ markedly in the macro- and micromorphological features and ecology.
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 niveosulcata (LE 313329, holotype, photo by O. Morozova). Scale bars = 1 cm.
Fig. 3 Microscopic features of Volvariella niveosulcata (LE 313329, holotype). A. Pileipellis. B. Basidia. C. Cheilocystidia. D. Spores. E. Pleurocystidia. Scale bars = 10 μm.
Malysheva, E., Malysheca, V., Alexandrova, A. & Morozova, O. 2019 –Observations on Pluteaceae in Vietnam. 1. New species and new records of Volvariella. Phytotaxa 408(40): 233–254.
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