Volvariella sulcata Knudsen & Kaygusuz, 2024

Volvariella sulcata Knudsen & Kaygusuz , sp. nov. ( Figs. 5–7 View FIGURE 5 View FIGURE 6 View FIGURE 7 )

MycoBank:— MB846139

Holotype:— DENMARK. Central Jutland , Skanderborg, Skanderborg Stadion, on soil in man-made habitats, 09 Sep 2002, leg. Jens Mårbjerg JM02-31 (holotype C-F-100386!, isotype in ISUF). GenBank accession nos.: ITS-PQ058320, 28S-OP663316.

Etymology:— sulcata (Latin) , refers to the sulcate pileus margin.

Description:— Pileus 7.0–14.0 mm diameter, at first convex, becoming broadly convex to broadly campanulate with maturity, without umbo, surface dry, white to dirty whitish, non-hygrophanous, glabrous, striate when young, later becoming plicate-striate from the margin to near the centre. Lamellae free, thin, distant, ventricose, up to 2.5 mm broad, whitish to dirty pink, with concolorous, minutely fimbriate edge. Stipe 8.0–12.0 × 1.0– 1.8 mm, cylindrical, slightly broadened downward, surface pure white, smooth. Volva fragile, saccate, 3.0 × 5.0 mm high, pure white, irregularly lobed. Context white. Smell and taste indistinct.

Basidiospores [172/4/3] (5.8–)6.0–8.0(–9.8) × (4.4–)4.5–5.5(–6.4) µm, Lm × Wm = 7.1× 4.9 µm, Q = (1.3–)1.4– 1.5(–1.6), Qm = 1.4, ellipsoid to broadly ellipsoid, smooth, thick-walled, with or without a large central (oil)drop, non-amyloid, non-cyanophilic. Basidia 22–40 × 9.0–11.5 µm, narrowly to broadly clavate with inflated in the middle, two to four-sterigmate, occasionally one-sterigmate, with homogeneous or granular contents, thin-walled. Lamellar margin sterile. Pleurocystidia (45–)50–81(–90) × (9.0–)12.0–17.0(–21) µm, moderately abundant, predominantly narrowly lageniform to lageniform, often with long cylindrical neck, and subcapitate to obtuse apex, sometimes with up to 30 µm long pedicel, rarely utriform, near lamellar edges mostly narrowly to broadly fusiform or flexuose, sometimes with sinuous or geniculate neck and bulbous apex, thin-walled, hyaline. Cheilocystidia (27–)40–75(–80) × (8.5–)10–21(–25) µm, abundant, variously shaped, narrowly utriform to utriform, and fusiform to broadly fusiform to lageniform, with 5.0–12.0 µm wide or obtuse to subcapitate apex, short to long pedicellate, rarely clavate, thin-walled, hyaline. Pileipellis a cutis, consists of elongate narrowly cylindrical to cylindrical, ellipsoid to broadly ellipsoid or even subglobose and utriform elements of (20–)30–90(–115) × (5.5–)10–30(–45) µm, mostly in chains, hyaline, non-gelatinous hyphae, with thin, smooth walls. Stipitipellis a cutis, consists of elongate cylindrical elements of 5.0– 12.0 µm wide, thin-walled, hyaline. Caulocystidia consists of cylindrical hyphae, 70–150 × 6.0–8.0 µm, thin-walled, hyaline. Clamp connections absent in all tissues examined.

Habit, habitat, and phenology: —In groups on soil in man-made habitats, incl. here a running course on a stadium, and two collections in hothouses. Most likely previously confused with the similar V. pusilla (Pers.) Singer. We are convinced that the pictures in Cetto (1984) from Italy and in Uzelac (2009) from Serbia are good representations of this small, characteristic species. The few collections point to a thermophilic species, possibly introduced in Denmark.

Distribution: —Only known from a few places in Denmark.

Additional collections examined: — DENMARK. North Zealand region, Nybo S of Kvistgård, on soil in man-made habitats, 11 August 1983, leg. D. Kreilgård s.n. (as V. pusilla , det. H.F. Gøtzsche) (C-F-108932); ibid., Southwestern Zealand, Flakkebjerg, Toftø Forsøgsgartneri, in hothouses, 07 July 1984, leg. S. Klug-Andersen s.n. (as V. pusilla ) (C-F-108933).

Discussion:— Volvariella sulcata is characterized by its smaller basidiomata often with a short stipe, sulcate-striate pileus margin, the number of lamellae being 35–45, ellipsoid basidiospores, lageniform pleurocystidia with a long neck and pedicel, highly variable cheilocystidia, a pileipellis including very short and broad elements, and a preference for man-made habitats.

The phylogenetic analyses inferred from the combined ITS/28S data set ( Fig. 1 View FIGURE 1 ) reveal that Volvariella sulcata forms an autonomous lineage within the genus Volvariella . Morphologically, the species most closely resembling V. sulcata is V. pusilla (Pers.) Singer (1951: 401) . Described by Persoon in 1799, V. pusilla is recognized as the classical small Volvariella species in Europe, characterized as small and white basidiomata with a plicate margin ( Persoon 1799). Studies by Shaffer (1957) and Boekhout (1986, 1990) reported basidiospores measuring 6.3–7.8 × 4.0–5.4 µm, which are nearly identical to those of V. sulcata . The basidiomata of V. pusilla are slightly larger, with a pileus up to 30 mm in diameter and a generally longer (up to 50 mm in length) and broader (up to 5 mm in width) stipe. V. sulcata is generally more slender, and the number of lamellae, excluding lamellulae, is notably lower (35–45) in V. sulcata compared to approximately 60 in V. pusilla , as described by Kriglsteiner (2003). The pileipellis in V. sulcata includes inflated terminal cells ( Fig. 7 View FIGURE 7 ), which are absent in V. pusilla . Additionally, habitat preferences differ: V. sulcata has been found exclusively in thermophilic, man-made habitats on rich soil, whereas V. pusilla occurs in both man-made environments and natural habitats such as forests and calcareous meadows. The most critical factor distinguishing these species is the significant genetic divergence in their sequences, as evidenced by GenBank data. Consequently, we confidently describe V. sulcata as a new species, previously misidentified as V. pusilla .

Several species are morphologically related to Volvariella sulcata , including V. hypopithys (Fr.) Shaffer (1957: 572) , V. pellucida Shaffer (1963: 570) , V. reidii Heinem. (1978: 239) , V. striatula Peck (1895: 487) , and V. turcica O. Kaygusuz & H. Knudsen ( Kaygusuz et al. 2020: 580) . V. hypopithys differs from V. sulcata with its larger basidiomata (up to 50 mm in diameter), fibrillose to squamulose pileus with not striate margin, longer stipe (20–80 mm in long) with densely pubescent to villose surface, and significantly longer cheilocystidia (up to 124 µm) ( Shaffer 1957, Boekhout 1990). The North American V. pellucida differs by its diaphanous pileus, vinaceous buff to avellaneous volva that stains grey, and fusoid-ventricose or lageniform cheilo- and pleurocystidia ( Shaffer 1963). V. reidii is characterized by a pileus usually with a distinct central umbo, a stipe with brown tinges, much shorter basidiospores (on av. 4.8 × 3.7 µm), and longer cheilocystidia (up to 112 µm) ( Reid et al. 1977). The other species, V. striatula (as Volvaria striatula ), originally described from Indiana ( USA), also similar in having small white basidiomata with striate pileus margin, but differs by its membranous volva and larger subglobose basidiospores ( Peck 1895). V. turcica is distinguished by its white pileus with a pale ochre centre, an ochre-discolouring volva, notably shorter basidiospores (on av. 5.2 × 3.2 µm), and balloon-shaped to clavate cheilocystidia ( Kaygusuz et al. 2020).