Volvariella clavocystidiata Kapitonov & E.F. Malysheva, 2022

Malysheva, Ekaterina, Kapitonov, Vladimir & Malysheva, Vera, 2022, A new species of Volvariella (Pluteaceae, Basidiomycota) from Western Siberia, Russia, Phytotaxa 538 (2), pp. 141-148 : 144

Volvariella clavocystidiata Kapitonov & E.F. Malysheva , sp. nov. ( Fig. 1 )

MycoBank MB 841252

Diagnosis: —The swamp habitat, silky fibrillose whitish pileus, clavate cheilo- and pleurocystidia, and basidiospores on average 6.6 × 4.8 µm, as well as exclusive the nrITS and nrLSU sequence data, are the key characters for separating V. clavocystidiata from other species of the genus.

Type: — RUSSIA. Tyumen Region, Vagayskiy District, vicinity of Rjabovo village , N57,16051°, E70,29086°, lowland swamp, 23 July 2020, V . Kapitonov 313639 (holotype LE!, GenBank OK256901 - ITS and OK256955 - LSU) .

Etymology: —The name refers to the shape of hymenial cystidia.

Basidiocarps small. Pileus 15–22 mm diam., at first hemispherical, then convex to plano-convex or plano-umbonate with low broad umbo, with serrate-sulcate margin, non-hygrophanous, surface not viscid, silky fibrillose, whitish or silvery-white, with yellowish or cream centre. Lamellae subcrowded, free, slightly ventricose, initially whitish then pink, edge even, entire concolorous. Stipe 25–35 × 1.5–5.0 mm, cylindrical, somewhat broadening towards base, smooth or slightly pruinose, whitish. Context in pileus and stipe white. Volva well developed, not voluminous (up to 7 mm high), saccate, lobate, felt-membranous, white or cream. Smell and taste indistinct.

Basidiospores 6.0–6.9(8.2) × (4.1)4.4–5.4 µm, av. = 6.6 × 4.8 µm, Q = (1.17)1.26–1.49(1.60), Q av = 1.37 (n=120), ellipsoid to broadly ellipsoid or ovoid, smooth, thick-walled. Basidia 24.0–41.0 × 7.0–11.3 µm, av. = 30.6 × 8.8 µm (n = 60), (2-) 4-spored, narrowly to broadly clavate, thin-walled. Cheilocystidia (30.6)34.7–52.3(63.6) × (11.3)14.0– 23.5(33.3) µm, av. = 44.1 × 18.6 µm (n = 60), numerous, narrowly to broadly clavate or broadly utriform, slightly thick-walled. Pleurocystidia (40.0)44.0–65.0(73.7) × (14.0)15.6–38.2(41.7) µm, av. = 53.0 × 25.3 µm (n = 60), rather numerous, similar to cheilocystidia in shape. Pileipellis a cutis, consisting of septate and elongate, non-gelatinous, slightly thick-walled hyphae 8–15 μm wide, with terminal cylindrical elements up to 23 μm wide. Stipitipellis a cutis, composed of long, cylindrical, hyaline hyphae, 10–16 µm wide. Caulocystidia absent. Clamp connections absent in all tissues examined.

Habitat and known distribution: —Growing solitary in waterlogged soil among green mosses and decaying remains of herbaceous plants, in lowland bog (with Carex and Equisetum ). So far known only from type locality.

The basidiocarps were found in a rather unusual ecotope for the Volvariella , viz. a lowland minerotrophic sedgehorsetail-moss bog with Equisetum fluviatile L. and Carex rostrata Stokes dominating in the grass layer. The moss cover is dominated by Drepanocladus aduncus (Hedw.) Warnst. and Plagiomnium ellipticum (Brid.) T. Kop. The sparse tree-shrub layer is formed by individual trees of Betula pubescens Ehrh. and Salix pentandra L., as well as shrub willows ( Salix cinerea L.).

Specimen examined: — Holotype.

Notes: — Volvariella clavocystidiata is characterized by its small basidiocarps with silvery-white, silky fibrillose pileus, whitish volva, predominantly clavate hymenial cystidia, and swamp habitat. Volvariella hypopithys (Fr.) Shaffer (1957: 572) differs in the generally larger basidiocarps, entirely pubescent stipe, fibrillose-hairy pileus and slightly narrower basidiospores (3.5–5.0 µm following Boekhout 1990). The new species also resembles Volvariella pusilla (Pers.) Singer (1951: 401) based on macroscopic characters but the latter differs in longer (45–85 µm) fusiformlageniform hymenial cystidia ( Boekhout 1990). Another morphologically similar species, Volvariella paludosa Kapitonov & E.F. Malysheva (2020: 455) , can be distinguished by its larger basidiocarps with pileus 40–70 mm, larger basidiospores (7.6–9.7 × 4.9–6.7 μm) and lageniform cheilocystidia ( Crous et al. 2020).

Two North American species, V. alachuana (Murrill 1942: 145) Shaffer (1957: 568) and V. smithii ( Shaffer 1957: 568) , are also characterized by silky fibrillose whitish pileus and white or pale-coloured volva. However, they differ in their ecological preferences (both occur in woods), V. alachuana has variable hymenial cystidia (lanceoloid, dumbbellshaped), and V. smithii has smaller spores (4.7–7.0 × 3.1–3.9 μm) and fusoid pleurocystidia with acute apex ( Shaffer 1957).

In the phylogenetic tree based on nrITS and nrLSU sequences ( Fig.2 ), the phylogenetic position of V.clavocystidiata was clearly separated from other known species of Volvariella ; it clustered with the sequence of Volvariella sp. KR349630 from India but without any statistical support. In addition, the latter collection is likely to represent a different species due to large molecular differences between them (with percentage of genetic divergence in their nrITS sequences>15 %).

Figures

FIGURE 1.—Morphological features of Volvariella clavocystidiata. A. Mature basidiocarp. B. Basidia. C. Spores. D. Pileipellis. E. Cheilocystidia. F. Pleurocystidia.All from holotype (LE 313639). Scale bars = 1 cm (for A) and = 10 μm for B–F.

FIGURE 2.—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 accession numbers from GenBank or UNITE databases. For taxon in bold the sequences are generated in present study.