Volvariella guttulosa E.F. Malysheva & A.V. Alexandrova
Index Fungorum number: IF 831058; MycoBank number: MB 831058
Basidiocarps tiny. Pileus 5–10 mm diam., at first ovoid or bullet-shaped, becoming convex to plano-umbonate with small low umbo, with serrulate, thin, non-striate margin fringed with fluffy fibrils; non-hygrophanous; surface not viscid, at young age covered with numerous clear water droplets; pure white, with creamy centre; covered with appressed and radially arranged hairs. Lamellae distant, free, with solitary lamellulae, slightly ventricose, dirty pink, unevenly coloured with spots, with slightly sinuous edge. Stipe 10–15 × 0.6–1 mm, cylindrical, slightly broadened downward, solid, white; surface gently tomentose, with numerous small humidity drops over the surface. Volva rather thick, saccate, pure white, irregularly lobed, with felted outer surface. Context white. Smell and taste indistinct. (Fig. 2)
Basidiospores [30, 1, 1] (5)6–7(8) × (3.5)4–4.7 μm (Lav = 6.5 μm, Wav = 4.2 μm, Q = 1.14–1.80, Q* = 1.56), broadly ellipsoid, ellipsoid or subamygdaliform, some ovoid or subcylindrical, hyaline in KOH, thick-walled. Basidia 17–22 × 7–9 μm, (3-)4-spored, clavate with a prominent medial constriction. Cheilocystidia 35–55 × 9.5–12(16) μm, rather numerous, predominantly lageniform, pedicellate, with sinuous neck and obtuse apex, thin-walled, hyaline in 3% KOH. Pleurocystidia 45–70 × 10–14(17) μm, abundant, in general similar to cheilocystidia but more inflated, occasionally fusiform and with round, almost subcapitate, apex, thin-walled, hyaline in 3% KOH. Lamella trama composed of hyaline hyphae 4–8 μm wide, thin-walled. Pileipellis a cutis, composed of slightly thick-walled, nongelatinous, hyaline hyphae, 10–15 μm wide; terminal elements cylindrical, repent or slightly ascending. Stipitipellis a cutis, similar to pileipellis, hyphae 7–12 μm wide; hairs present at only basal part, cylindrical, 95–150 × 11–15 μm, hyaline, thin-walled. Clamp connections absent in all tissues examined. (Fig. 3)
Habitat and known distribution: Solitary, on dead wood. So far only known from the type locality.
Specimen examined: Holotype.
Notes: Volvariella guttulosa is characterized by tiny pure white basidiocarps with hairy pileus and tomentous stipe, usually entirely covered with small droplets of moisture, medium-sized basidiospores (Lav = 6.5 μm, Wav = 4.2 μm), presence of numerous hairs on stipe surface and lignicolous habit. This new taxon is quite different from other Volvariella species forming tiny white basidiocarps: Volvariella niveosulcata generates its basidiocarps on soil, and besides, it has almost smooth, silky fibrillose pileus, longer stipe, larger basidiospores (7–9 × 5.5–6.5 μm), clavate or utriform cheilocystidia and no hairs on stipe. Volvariella pusilla differs by larger basidicarps, which are not usually pure white, differently shaped hymenial cystidia and terrestrial habitat (Shaffer 1957, Boekhout 1990). Volvariella pellucida also differs by its terrestrial habitat, as well as vinaceous buff volva, fusoid-ventricose or lageniform cheilo- and pleurocystidia, and wider (5–6 μm) ovoid basidiospores (Shaffer 1962). Volvariella delicatula and V. liliputiana resemble Volvariella guttulosa in macroscopic features, but the main distinguishing character is their subglobose basidiospores (Hennings 1901, Massee 1912).
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 Immature and mature basidiocarps of Volvariella guttulosa (LE 313326, holotype, photos by A. Alexandrova). Scale bars = 1 cm.