Volvariella similis Knudsen & Kaygusuz, 2024

Volvariella similis Knudsen & Kaygusuz , sp. nov. ( Figs. 2–4 View FIGURE 2 View FIGURE 3 View FIGURE 4 )

MycoBank: — MB846138

Holotype:— DENMARK. North Zealand , Risø, on lawn, at 56°86′N, 9°85′E, 03 Dec 2003, leg. David Boertmann DB 2003/004 (holotype C-F-84720!), GenBank accession nos.: ITS-MK770141, 28S-OP663309.

Etymology:— similis (Latin) —similar, referring to the macroscopic similarity to Volvariella murinella .

Description:— Pileus 20–55 mm diameter, at first conical to convex, becoming low convex with or without an umbo, non-striate margin, surface dry, non-hygrophanous, brown or brownish grey, darker at centre. Lamellae free, thin, crowded, ventricose, up to 3.0 mm broad, whitish to dirty pink, with concolorous margin. Stipe 30–80 × 4.0–7.0 mm, cylindrical, slightly broadened downward up to 9 mm, pubescent when young, surface grey, smooth. Volva small, up to 8 mm high, irregularly lobed, felt-membranous, brown. Context white. Smell and taste indistinct.

Basidiospores [170/4/3] (6.0–)6.5–8.0(–10.0) × (3.9–)4.0–4.5(–5.1) µm, Lm × Wm = 7.5 × 4.4 µm, Q = (1.5–)1.6–1.9(–2.0), Qm = 1.7, ellipsoid to elongate, smooth, with or without a large central (oil) drop, non-amyloid, non-cyanophilic, hyaline, slightly thick-walled. Basidia 24–34 × 7.5–10.5 µm, narrowly to broadly clavate with often inflated in the middle, two to four-sterigmate, occasionally one-sterigmate, with cyanophilic content, thin-walled. Lamellar margin sterile. Pleurocystidia (37–)48–72(–86) × (5.0–)7.0–13(–20) µm, numerous, predominantly broadly lageniform to fusiform with a tortuose or curved apical appendage up to 27 µm long, near lamellar edges mostly filamentous-flexuous irregularly subcylindric to narrowly clavate, lageniform or fusiform, either obtuse, mucronate, and capitate, or with an elongate apical appendage, sometimes slightly narrow near base, hyaline, thin-walled. Cheilocystidia (35–)40–70(–100) × (10–)12–30(–40) µm, abundant, extremely variable in size and shape, clavate to broadly subutriform (with obtuse or subcapitate apex) to broadly fusiform, oblong ellipsoid or cylindrical, sometimes with finger-like appendage, hyaline, thin-walled. Pileipellis a cutis, with terminal elements 35–355(–370) × 6.5–27 µm, individual elements cylindrical, with gradually tapering towards apex, short- to long-celled parallel non-gelatinous hyphae, smooth, hyaline, thin-walled. Stipitipellis a cutis, composed of narrow cylindrical cells, 4–10 µm wide, hyaline, thin-walled. Caulocystidia absent. Clamp connections absent in all tissues examined.

Habit, habitat, and phenology: — The Danish collections were growing solitary or a few together in grass and on lawns. They are from May , November and December perhaps avoiding the warmest months. Distribution : — So far only known from a few localities in Denmark. Additional collections examined:— DENMARK. North Zealand , Sorgenfri , on lawns, 03 Nov 2000, leg. Betty Klug-Andersen (C-F-42306) ; ibid., North Jutland, Buderuplund-Buderupholm Dambrug , on soil in grassy path next to wet heathland, 23 May 2009, leg. Thomas Laessøe (TL-13596) (C-F-86457) ; ibid., North Jutland, Høstemark Skov S of Mou, on lawns, 12 Sep 1993, leg. Søren Hansen & Jan Vesterholt JV 93-852 (as V. pusilla var. taylorii ) (C-F-28631) .

Discussion:— Volvariella similis is characterized mainly by small basidiomata with a brownish pileus, a grey stipe without caulocystidia, pleurocystidia composed of two types of elements, clavate to broadly subutriform (with an obtuse or subcapitate apex) to broadly fusiform, oblong ellipsoid or cylindrical cheilocystidia, and pileipellis composed of cylindrical, gradually tapering, short- to long-celled parallel elements.

Phylogenetic analyses based on nrITS/nrLSU rDNA ( Fig. 1 View FIGURE 1 ) show that V. similis is sister to V. paludosa and is clustered in a clade with V. dunensis , V. murinella , and V. taylorii . However, the percentage of similarity of nrDNA ITS sequences of V. similis to V. dunensis , V. murinella , V. paludosa , and V. taylorii is 94.8%, 87.0%, 96.5%, and 86.5%, respectively. Morphologically V. paludosa , originally described from Russia, differs from V. similis by its larger basidiomata (up to 70 mm in diameter) and stipe (up to 80 mm in length), white volva, slightly larger basidiospores (on average 8.7 × 5.6 µm) with a lower Q-value (Qm = 1.5), shorter cheilocystidia (up to 67 µm), utriform or broadly clavate pleurocystidia without elongate apical appendage, and its habitat in a rich fen ( Crous et al. 2020). V. dunensis , described from Spain, differs from V. similis by a larger basidiomata (up to 100 mm in diameter), grey to grey brown pileus, shorter basidiospores (on av. 7.3 × 5.2 µm) with a lower Q-value (Qm = 1.4), longer cheilo- and pleurocystidia (up to 120 and 112 µm, respectively) without apical appendages, and a habitat usually in dunes ( Ludwig 2007, Justo & Castro 2010, Crous et al. 2020). V. murinella has larger basidiomata (up to 70 mm in diameter) with a more greyish pileus, a longer stipe (up to 80 mm in length), usually a grey volva, much shorter basidiospores (on av. 7.3 × 4.7 µm) with a lower Q-value (Qm = 1.5), and pleurocystidia without apical appendage ( Orton 1960, 1974). V. taylorii differs by the subviscid pileus, glabrous volva, even, not striate pileus margin, broader basidiospores (5.5–8.7 × 4.0–6.0 µm), and fusoid-ventricose, clavate, or ovoid pleurocystidia ( Bresadola 1929, Orton 1974, Boekhout 1990, Crous et al. 2017).

In Volvariella View in CoL several species have a pileus with grey tinges. Some, such as V. volvacea (Bull.) Singer View in CoL and V. nigrovolvacea Kosina (1974: 129) View in CoL , are larger, often> 50 mm in pileus width, and others, like V. caesiotincta P.D. Orton (1974: 319) View in CoL and V. morozovae E.F. Malysheva & Aleks. ( Crous et al. 2017: 343) View in CoL , have their habit on wood. V. cinerascens (Bres.) M.M. Moser (1967: 177) View in CoL differs in having a pileus with striate margin, grey volva, white stipe, and narrower basidiospores (6.5–7.3 × 3.0–3.5 µm) ( Bresadola 1929, Orton 1974). V. fuscidula (Bres.) M.M. Moser ex Shaffer ( Shaffer 1963: 566) View in CoL differs in having a viscid pileus with striate margin and a darkening stipe ( Bresadola 1929, Shaffer 1963, Orton 1974).