Caballero, Justo & L.A. Parra, 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 : 57-59

18. Volvariella glaucocephala F. Caballero, Justo & L.A. Parra , sp. nov. ( Fig. 26 ).

MycoBank: MB 856535

Typification:— Holotype: SPAIN. Madrid, Madrid city, parque del Oeste, 40.433079, -3.729172, under Cedrus atlantica , in a grassy area with a fairy ring of Agaricus arvensis , on ground rich in mycelium of this species, among the basidiomes of A. arvensis , 20 August 2005, L.A. Parra, AH60251! (Isotype: LAP 188).

Etymology:—From the Greek “ glaukos ” a bluish grey variable colour, and “ kephale ” head”, for its glaucous pileus surface.

Diagnosis:— Volvariella glaucocephala is characterized by its bluish grey pileus surface, sometimes with olive brown tones, saccate, usually dark grey volva, small spores (avl × avw = 6.3 × 4.1 μm), and fruiting among basidiomes of Agaricus arvensis .

Description:— Pileus 18–35 mm diam., ovoid when young, expanding to conico-convex, convex and plano-convex in older specimens, with a central umbo; surface smooth or radially fibrillose, notably hygrophanous, varying from grey to bluish grey or grey-brown, darker (sometimes almost black) at centre, sometimes with olive brown tones; margin smooth or radially striate. Lamellae crowded, free, broadly ventricose, white when young, becoming salmon pink or pinkish brown with age; edge entire, or irregular, white or concolourous. Stipe 35–68 × 3–6 mm, clavate, slightly widening towards the base (up to 15 mm wide), straight or slightly sinuose; surface white, sometimes with brown tints at the apex, smooth, pubescent or slightly fibrillose. Volva membranaceous, saccate, white to dark grey, with 3–5 lobes. Rhizomorphs not observed. Context white; smell not recorded.

Basidiospores (n=94, c=3) 5.4–8.4 × 3.6–5.3 μm, avl × avw = 6.3 × 4.1 μm, Q = 1.28–1.93, avQ = 1.54, broadly ellipsoid to oblong, thick-walled, with barely distinct hilar appendage. Basidia 15–30 × 7–12 μm, tetrasterigmate, clavate, subclavate or subcylindrical. Lamella edge heterogeneous. Cheilocystidia common, 38–95 × 10–22 μm, most lageniform or broadly lageniform, with a rounded to subcapitate apex, less commonly,utriform, clavate or subcylindrical, some with a secondary septum in upper part. Pleurocystidia scarce, 55–88 × 16–25 µm, most lageniform or utriform. Pileipellis a cutis or an intermediate cutis-trichoderm, with terminal elements 7–33 μm wide, often constricted at the septa, with diffuse intracellular brown or olive-brown pigment; also, with spherical or subspherical elements, 21–28 × 17–22 µm, sometimes attached to the sides of the cylindrical hyphae. Stipitipellis a cutis or a cutis-trichoderm in the upper part of the stipe, with cylindrical hyphae 3–14 μm wide. Volva composed of interwoven, cylindrical hyphae, 3–25 μm wide, with common septa; on the external surface organized as a trichoderm. Clamp connections absent in all parts examined.

Habit, habitat, and phenology:—Often gregarious in small groups. Terrestrial, growing under Cedrus atlantica , in a grassy area with a fairy ring of Agaricus arvensis on ground rich in mycelium of this species, sometimes among the basidiomes of A. arvensis and sometimes without Agaricus fructifications. August to November.

Distribution:—Known from a single site in the “parque del Oeste” in Madrid capital ( Spain).

Additional collections examined:— SPAIN. Madrid, city of Madrid, Parque del Oeste, 40.433079, -3.729172, elev. 600 m, under Cedrus atlantica , in a grassy area with a fairy ring of Agaricus arvensis , on ground rich in mycelium of this species, among the basidiomes of A. arvensis , 6 August 2005, L.A. Parra, LOU-Fungi 18924); ibid., under Cedrus atlantica , in a grassy area with a fairy ring of Agaricus arvensis , on ground rich in mycelium of this species, without basidiomes of A. arvensis , 4 November 2006, L.A. Parra, LAP 189.

Observations:—The description is based on three collections from the same collecting site.

Volvariella glaucocephala appears in the phylogenetic analyses as closely related to V. hypopithys ( Fig. 4 ). However, morphologically, it differs from V. hypopithys , as accepted here, in the grey-blue colours of the pileus, the slightly narrower basidiospores, (avQ = 1.36 in V. hypopithys ), and the habitat under Cedrus atlantica on ground rich in mycelium of Agaricus arvensis .

While other European species have predominantly grey colours in the pileus, the particular grey-blue tint (sometimes with olive brown tones) observed in V. glaucocephala has not often been recorded for other taxa. In Europe, V. caesiotincta and V. terrea , might present bluish tinges in the pileus but both taxa appear in the phylogenetic analyses clearly separate from V. glaucocephala ( Fig. 1 ). Volvariella caesiotincta has larger basidiomes with a pileus up to 70(– 120) mm diam., the cheilocystidia are often provided with digitate projections, and it often grows directly connected to wood. Volvariella terrea has larger basidiomes (pileus up to 80 mm diam.), longer spores, wider pleurocystidia, and occurs in grassy areas among basidiomes of Agaricus xanthodermus . Similarly, V. glaucocephala occurs among basidiomes of Agaricus arvensis and it has been observed that from 2006 onwards no additional collections were found, despite the fact that the collection site was visited several times each year. In the same period not a single basidiome of Agaricus arvensis was seen. Musumeci and Riva (2007) suggest that the association of V. terrea with Agaricus xanthodermus is indicative of a parasitic relation, and our observations on V. glaucocephala show a similar pattern with A. arvensis . However, more collections should be studied to unequivocally conclude that these two Volvariella species are in a parasitic relationship with Agaricus species.

Figures

FIGURE 1. Best tree from the Maximum Likelihood analysis of the ITS dataset of Volvariella: general overview with collapsed terminal clades (except V. ranulicystis). BS ≥ 70 % and PP ≥ 0.90 are shown on or below the branches. The length of branches marked with “/” has been reduced to accommodate graphical representation. Newly described taxa are highlighted in red.

FIGURE 4. Best tree from the Maximum Likelihood analysis of the ITS dataset of Volvariella: detailed view of the lineage including V. hypopithys and related taxa. BS ≥ 70 % and PP ≥ 0.90 are shown on or below the branches. Newly described taxa are highlighted in red.

FIGURE 26. Volvariella glaucocephala. A–C. Basidiomes. A, C. (AH60251, holotype); B. (LAP189). D–J. Microscopic characters (AH60251, holotype). D. Cheilocystidia; E. Pleurocystidia; F, Spores; G. Pileipellis hyphae; H. Volva hyphae; I–J. Stipitipellis. Bar: (D–F, H) = 10 µm; (G, I, J) = 100 µm. Photos by L.A. Parra (A–C), F. Caballero (D–J).