Rubroboletus pruinosus Salna Nanu & T. K. A. Kumar, sp. nov.

Index Fungorum number: IF 902411; Mycobank number: MB 902411; Facesoffungi number: FoF 14043; Fig. 1

Etymology – The epithet “pruinosus” refers to the pruinose nature of pileus and stipe surface.

Holotype – ZGCSN100

Basidiomata small- to medium-sized. Pileus 15–25 mm in diam., hemispherical when young becoming applanate at maturation; surface grayish red to dark red, dry, pruinose, dark immediately turning blue to dark blue on bruising. Pileal context 5–15 mm thick, cream to white, turning blue to dark blue on bruising. Hymenophore somewhat depressed around stipe apex; surface pinkish to reddish, fading with aging, immediately changing to blue with bruising; pores round to angular, 1–2 per mm; tubes up to 3.5 mm long, yellowish, rapidly changing to blue on bruising. Stipe 20–40×5–15 mm, reddish, paler towards the middle, with scattered darker pruinose patches, changing to dark blue on bruising, subcylindrical, broadening towards the base. Stipe context pale yellow, turning blue quickly when cut. Basal mycelium white. Odour not distinct. Spore print not obtained.

Basidiospores 8–10 × 4.5–5.5 µm (Q = 1.6–2 µm, Qm = 1.74 µm), broadly ellipsoid, smooth, with a large guttule, thin- to thick-walled, hyaline to pale yellow, inamyloid. Basidia 24–31 × 9–13 µm, clavate, thin-walled, 4-spored, hyaline, inamyloid, sterigmata up to 4 µm long. Pleurocystidia 28–60× 7–9 µm, lageniform, mostly with apical protrusions up to 11 µm long, thin-walled, yellow or yellowish brown in water, inamyloid. Cheilocystidia 26–40×6–10.5 µm, lageniform, utriform, abundant, thin-walled, hyaline to pale yellow in water, inamyloid. Pileipellis a cutis disrupted by trichodermial patches of ascending to erect hyphae with cylindrical end cells; end cells 2–6 µm wide, thick-walled (wall thickness up to 1.5 µm), yellowish to bright yellow in water; hyphae 3–6 µm wide, thick-walled (wall thickness up to 1.5 µm), with reddish brown plasmatic pigment. Pileal trama interwoven; hyphae 4–10 µm wide, thin-walled, hyaline to pale yellow, inamyloid. Stipitipellis a cutis disrupted by trichodermial patches; terminal elements 2–4 µm wide, slightly thick-walled (wall thickness up to 0.5 µm), cylindrical, with brownish yellow plasmatic pigments. Stipe trama interwoven, hyphae 3–10 µm, hyaline, thin-walled.

Ecology and distribution – on soil, scattered under Xanthophyllum arnottianum Wight.

Material examined – India, Kerala State, Kollam District, near Ammayambalam temple, 10 August 2021, Salna Nanu (ZGCSN100, holotype).

GenBank numbers – ZGCSN100: ITS = OQ504748: LSU=OQ472490: RPB2=OQ689073

Notes – Rubroboletus pruinosus is characterized by basidiomata with grayish red to dark red, pruinose pileus, pinkish to reddish pore surface, yellowish tubes, colour change of the pileal and stipe context to blue immediately on bruising, pruinose stipe surface, medium-sized basidiospores, and a pileipellis that is basically a cutis disrupted by trichodermial patches. Rubroboletus pruinosus differs from the closely related R. legaliae in having pinkish to reddish pore surface, pruinose stipe surface, smaller basidiospores, and the absence of caulocystidia. A comparative study of the ITS, 28S and rpb2 gene sequences reveals its genetic distinction. Rubroboletus legaliae shows resemblances with R. pruinosus in having depressed hymenial region around the stipe apex,yellowish tubes, colour change of the pileal context to blue whenbruised, and pleurocystidia and cheilocystidia with identical shapes and dimensions. However, R. legaliae differs in having larger basidiomata, reticulated stipe surface, larger basidiospores (10–15 ×4.5–5 µm), pileipellis that is an intricate trichodermium and by the presence of caulocystidia. Rubroboletus rhodosanguineus shows similar characters with R. pruinosus like pileus colour, context of the pileus and stipe changing to blue when hurt and subcylindrical stipe. However, R. rhodosanguineus has a smell of overripe fruit, yellowish pileal context, glabrous pileal surface and is mostly distributed in North and Central America and Europe.

Phylogenetically, R. pruinosus is clustering as a separate taxon within the Rubroboletus clade of the Pulveroboletus group in the Boletaceae family and is distinct from all other Rubroboletus species. The species is described here as novel based on the molecular and morphological evidence.

Figure 1 – Rubroboletus pruinosus (ZGCSN100, holotype). A, B, C, D, E Basidiomata. F Basidiospores. G Basidia. H Pleurocystidia. I Cheilocystidia. J Pileipellis. K Stipitipellis Scale bars: A, B, C, D, E=10 mm, F, G, H, I=10 µm, J, K=20 µm