Caballero, Justo & C. Roqué, 2025

Caballero, Fernando, Justo, Alfredo, Parra, Luis A., Angelini, Claudio, Consiglio, Giovanni, Dovana, Francesco, Ferisin, Giuliano, Kaygusuz, Oğuzhan, Knudsen, Henning, Llimona, Xavier, Muñoz, Guillermo, Daniëls, Pablo P., Pérez-De-Gregorio, Miquel À., Ševčíková, Hana, Valverde, Andrés & Vizzini, Alfredo, 2025, Taxonomic and phylogenetic overview of the genus Volvariella (Volvariellaceae), with a focus on European species, Phytotaxa 680 (1), pp. 1-85 : 61

20. Volvariella graminicola F. Caballero, Justo & C. Roqué , sp. nov. ( Fig. 28 ).

MycoBank: MB 856537

Typification :— Holotype: SPAIN. Girona : Baix Empordà , Camí dels Plans, in a grassy area, 2 October 2003, C. Roqué, AH60252! (Isotype: CR02102003-5).

Etymology:—From the Latin “ graminis ” of grasses and “- cola ” dweller, by its habitat in grassy places.

Diagnosis:— Volvariella graminicola is characterized by its small basidiomes, with overall pure white colours; it is morphologically very similar to all other small, white species. The nrITS sequences of V. graminicola differ in 9 changes from those of its closest relative, V. deceptiva .

Description:— Pileus 10–20 mm diam., convex when young, expanding to conico-convex, without an umbo; surface fibrillose or covered in small squamules; not hygrophanous, white overall, pale yellowish at centre in older specimens; margin smooth, slightly exceeding the lamellae and irregular. Lamellae moderately crowded, free, broadly ventricose, white when young, becoming salmon pink or pinkish brown with age; edge entire, or irregular, concolorous or white. Stipe 30–45 × 4–7 mm, cylindrical, slightly widening towards the base, straight or slightly curved; surface white, smooth to finely pubescent in upper part. Volva membranaceous, saccate, fragile, white, with 2–3 lobes; rhizomorphs not observed. Context white, thin, with indistinct smell.

Basidiospores (n=50, c=2) 6.3–7.1(–9.0) × 4.6–5.4 μm, avl × avw = 6.7 × 4.9 μm, Q = 1.3–1.5, avQ = 1.4, ellipsoid, thick-walled, with barely distinct hilar appendage. Basidia 27–36 × 8–10 μm, tetrasterigmate, clavate, subclavate. Lamella edge heterogeneous. Cheilocystidia common, 43–98 × 11–45 μm, lageniform, clavate, fusiform, some utriform, some with two round knobs in the upper part. Pleurocystidia scarce, 41–67 × 12–30 µm, similar to cheilocystidia. Pileipellis a cutis or an intermediate cutis-trichoderm, with terminal elements 5–28 μm wide, often constricted at the septa, most hyaline. Stipitipellis a cutis, or a cutis-trichoderm in the upper part of the stipe, with cylindrical hyphae 6–13 μm wide. Volva composed of interwoven, cylindrical hyphae, 4–32 μm wide, with common septa; individual segments often constricted at the septa. Clamp connections absent in all parts examined.

Habit, habitat, and phenology:—(Sub)gregarious. Terrestrial, among grass, in path edge rich in organic matter. October.

Distribution:— Spain, United Kingdom.

Additional collection examined:— UNITED KINGDOM. England: Little Wittenham (Oxforshire) on grass, 1997, R. Tofts, K(M)68813.

Observations:— Volvariella graminicola is very similar to other white species described here, especially to V. pusilla , to which it is also very close phylogenetically. It is not possible to separate these taxa based on morphology, and they can also fruit in very similar habitats (grassy areas). Basidiospore size is very similar in both species, average values are 6.7 × 4.9 µm for V. graminicola and 6.2 × 4.6 µm for V. pusilla . The shape and size of the cystidia show a similar degree of overlapping variation between both taxa, although V. graminicola does have some nodulose cystidia, which we have not observed in V. pusilla . The only morphological difference is the size of the basidiomes, up to 50 mm in V. pusilla and up to 20 mm in V. graminicola . Only DNA sequences offer a reliable way of separating V. pusilla , V. graminicola and most of the small white species described here, even those that are phylogenetically distant from each other. For a comparison with other small, white species see Tables 1 and 2.

Figures

FIGURE 28. Volvariella graminicola.A–B.Basidiomes (AH60252, holotype).C–G.Microscopiccharacters.C.Cheilocystidia (AH60252, holotype); D. Pleurocystidia (AH60252, holotype); E. Spores (K[M]68813); F. Pileipellis (K[M]68813); G. Volva hyphae (AH60252, holotype). Bar: (C–G) = 10 µm. Photos by C. Roqué (A–B), F. Caballero (C–G).