Volvopluteus fibrillobrunneus Enjam, E. Tarafder & A. R. Sherpa. sp. nov.

Figs 4, 5

Etymology.

The specific epithet “ fibrillobrunneus ” refers to the brown color with a fibrillose pileus surface.

Diagnosis.

Volvopluteus fibrillobrunneus differs from Volvopluteus earlei by its fibrillose brown pileus surface with larger basidiocarps (Pileus <50 mm in diameter Vp. earlei) and smaller basidiospores (8.3–11.5 × 5.1–7.1 μm).

Holotype.

India • West Bengal: North- 24 - Parganas district, Barasat, Near Kazibari Bus Stand, 22°44'45.5"N, 88°26'41.9"E, elev. 13.0 m, Scattered on the soil around with rich humus in broad-leaved forest, 18 September 2024, E. Hoque, AE- 37 / 2024 (CAL 2385, holotype).

Description.

Basidiomata medium to large. Pileus 80–97 mm diam., plano-convex to plane with age, low umbo at center, not viscid, dry, glabrous, innately radially fibrillose, striate, surface light brown (6 D 4), grayish brown (6 D 3) with grey (5 B 2) when young, dark blonde (5 D 4) center and birch grey (5 C 2) sides after maturity, becoming lighter grayish brown (5 F 3–5 E 4) towards the margin and yellowish brown (5 B 2–5 C 4) after dried; margin striate, radially fibrillose, slightly cracked with maturity, cream whitish squamulose present. Context 4 mm broad, white to grayish white (2 B 1). Lamellae free, approximately 10 mm broad, close to crowded, pinkish white (8 A 3–8 B 3), brownish gray (11 C 2) at maturity. Stipe 120–140 × 10–14 mm, central, cylindrical, solid, white, glabrous, not viscid, when young visibly broadening towards the base and in maturity with bulbous base enclosed in sac-like volva. Volva 15–19 × 8–10 mm, free from the stipe, saccate, membranous, 2–3 lobed, with a white to light brownish outer surface and whitish inner surface. Odor and taste indistinct.

Basidiospores (8.3 –) 8.5–9.6 (– 11.5) × (5.1 –) 5.4–6.3 (– 7.1) µm, [X mr = 8.65–9.43 × 5.88–6.25, X mm = 9.85 ± 0.92 × 6.30 ± 0.49 μm, Q mr = 1.36–1.75, Q mm = 1.57 ± 0.19, n = 30 basidiospores per 2 specimens], ellipsoid to elongate, smooth, hyaline to light yellowish in 5 % KOH, thin-walled, and apiculate. Basidia 25.7–45.6 × 9.8–11.9 µm, clavate, hyaline in 5 % KOH, smooth, with 2–4 prominent sterigmata, no clamp at base. Cheilocystidia 34–72 × 15–29 µm, hyaline in 5 % KOH, thick-walled, mostly clavate, forming a sterile layer at the lamellae edge. Pleurocystidia 53–75 × 14–21 µm, hyaline, thin-walled, lageniform rostrate with apical appendages. Pileipellis ixocutis, made up of hyphae 25–32 µm broad, hyaline, thin-walled, clamp connections absent. Stipitipellis as compactly arranged hyphae, 23–38 µm broad, thin-walled, clamp connections absent. Volva composed of septate interwoven cylindrical hyphae, thin-walled 9–13 µm broad, clamp connection absent.

Habitat and known distribution.

Scattered on the soil around with rich humus in a broad-leaved forest. So far, it is only known from India.

Additional specimens examined.

India • West Bengal: North- 24 - Parganas district, Barasat, near Kazibari Bus Stand, 22°44'45.5"N, 88°26'41.9"E, elev. 13.0 m, scattered on the soil around with rich humus in broad-leaved forest, 21 September 2024, E. Hoque, AE- 41 / 2024 (CAL 2386, paratype).

GenBank numbers.

CAL 2385 (holotype): nrITS = PX 764988, nrLSU = PX 764992; CAL 2386: nrITS = PX 764989, nrLSU = PX 764993.

Notes.

Volvopluteus fibrillobrunneus is characterized by a medium- to moderately large-sized (80–97 mm) pileus, entirely light brown to grayish brown, with a radially fibrillose surface; close to crowded lamellae colored pinkish white to brownish gray; a multi-lobed saccate volva with a white to light brownish outer surface and a whitish inner surface (Fig. 4); larger basidiospores measuring 8.3–11.5 × 5.1–7.1 μm; clavate to ventricose cheilocystidia measuring 34–72 × 15–29 μm; lageniform rostrate pleurocystidia with apical appendages measuring 53–75 × 14–21 μm; and habitat on rich humus soil (Fig. 5). Among macro-morphologically similar taxa (Table 5), Vp. earlei can be distinguished by its smaller basidiospores (11–16 × 8–11 μm), the presence of longer pleurocystidia (up to 110 μm), and the presence of cheilocystidia (Shaffer 1962; Justo and Castro 2010; Giannoni et al. 2018). Moreover, Volvopluteus earlei was originally described from Cuba (Murrill 1911) and later reported from the USA (Coker 1947), Mexico (Vázquez et al. 1989), Africa (Heinemann 1975), Argentina (Niveiro and Albertó 2012), Italy (Contu 2006; Giannoni et al. 2018), Spain (Justo and Castro 2010), Turkey (Kaygusuz et al. 2021), and India (Chouhan and Panwar 2021).

In the phylogenetic analyses (Fig. 1), Vp. fibrillobrunneus is placed as a sister group to Vp. platensis, originally described from China (Zhu et al. 2025), and can be distinguished from Vp. fibrillobrunneus by the smaller basidiomata (48–70 mm broad in Vp. platensis), a slightly brownish to grayish white pileus, and clavate to fusoid cheilocystidia (Zhu et al. 2025). Hence, here we introduce our collections as a novel species of Volvopluteus s. str., i. e., Vp. fibrillobrunneus, based on morpho-molecular analyses.