Inocybe rubrobrunnea K.P.D. Latha & Manim.

MycoBank number: MB 816736 Facesoffungi number: FoF: 2175

Etymology: referring to the reddish-brown colour of the pileus.

Holotype: CAL 1307

Basidiocarps small. Pileus 6–12 mm diam., somewhat hemispherical or paraboloid when young, becoming convex or plano-convex with a small umbo; surface reddish-brown (8E5, 8E6/OAC609, OAC610) when young, becoming dark brown (7F7/OAC621) at the centre and on the squamules, orange grey (6B2) elsewhere, appressed- to slightly recurved squamulose and appressed-fibrillose all over when young, becoming appressed- to recurved squamulose on and around the centre, appressed-fibrillose and rimulose towards the margin; margin initially incurved, becoming decurved to somewhat straight with age, crenate. Lamellae sinuate or emarginate, close, initially greyish-orange (6B3/OAC654), becoming brownish-orange (6C4/OAC695), up to 1.5 mm wide, with lamellulae of 3 lengths; edges fimbriate, whitish. Stipe 11–20 × 1–2 mm, central, terete, equal or slightly tapered towards the base, cartilaginous, solid; surface brownish-orange (6C3/OAC633), fading towards the apex, appressed-fibrillose all over, slightly pruinose at the apex; base slightly enlarged. Odour and taste not distinctive.

Basidiospores 7–9 × 5–6 (8.32±0.63 × 5.57±0.43) µm, Q = 1.2–1.7, Qm = 1.4, smooth, ellipsoid to slightly phaseoliform, slightly thick-walled, pale yellowish-brown. Basidia 18–27 × 9–12 µm, clavate, thin-walled, hyaline, 4-spored; sterigmata up to 3 µm long. Pleurocystidia absent. Lamella-edge heterogeneous. Cheilocystidia 17–44 × 6–15 µm, abundant, versiform: narrowly clavate, clavate, cylindrical, oblong, ellipsoid, fusiform, obovoid, cylindrical with a median constriction or with a subcapitate apex, occasionally septate, exuding some amorphous material at the apex, slightly thick-walled (up to 1 µm thick), hyaline or rarely with pale yellowish-brown, amorphous contents, occasionally with faint, hyaline encrustations. Lamellar trama subregular, composed of both narrow and inflated hyphae; hyphae 3–23 µm wide, thin- to slightly thick-walled, hyaline. Subhymenium pseudoparenchymatous. Pileus trama subregular; hyphae 6–27 µm wide, hyaline or pale yellow, thin-walled. Pileipellis a cutis often disrupted with bundles of tangled ascending hyphae towards the centre; hyphae 5–10 µm wide, with a pale brownish-yellow wall pigment and brown spiral encrustations. Stipitipellis a cutis composed of hyaline or pale yellow hyphae (3–10 µm wide), devoid of encrustations, frequently disrupted by bundles of loose, tangled hyphae towards the apex (2–6 µm wide), with a pale-yellow wall pigment and pale yellow spiral encrustations, thin- to slightly thick-walled, occasionally with yellowish-brown amorphous contents. Caulocystidia absent. Clamp connections observed on all hyphae.

Habitat: on soil, solitary or in small groups, near Hopea ponga (Dipterocarpaceae) trees.

Specimen examined: INDIA, Kerala State, Wayanad District, Muthanga, Muthanga Wildlife Sanctuary, 21 August 2013, K. P. Deepna Latha DKP142 (CAL 1307, holotype). GenBank numbers ITS:KX073583; LSU:KX073587; RPB2:KX073590.

Notes: Small basidiocarps with an appressed-fibrillose to squamulose pileus; a stipe with a slightly enlarged base and a fibrillose surface; smooth, ellipsoid to slightly phaseoliform basidiospores; a hymenium devoid of pleurocystidia; versiform cheilocystidia exuding some amorphous material at the apex; a cutis-type pileipellis disrupted with bundles of tangled ascending hyphae; and a cutis-type stipitipellis often disrupted by bundles of loose, tangled hyphae towards the apex are the diagnostic features of I. rubrobrunnea.

Following the key of Kobayashi (2002), I. rubrobrunnea keys out close to I. quercina Hongo, a species known from Japan, because of its reddish-brown pileus with almost similar size, shape and surface features, a whitish lamella-edge, a solid stipe with a fibrillose surface, almost similar-shaped basidiospores, the absence of pleurocystidia and the presence of cheilocystidia. However, the characters such as the adnexed lamellae that become red when cut, a longer stipe, larger basidiospores (8.2–10.8 × 4.8–5.5 µm) and basidia, smaller cheilocystidia devoid of encrustations, a cutis-type pileipellis lacking encrustations, the presence of caulocystidia and a strong odour of that species make it different from I. rubrobrunnea. Inocybe fuscospinulosa, a species originally described from Indonesia (Horak 1980b) and also reported from Sri Lanka (Pegler 1986), has a pileus with dark brown squamules, a whitish lamella-edge, basidiospores of similar size (7–9 × 4.2–5.5 µm) and shape and the absence of pleuro- and caulocystidia. However, that species differs in having larger basidiocarps with a campanulate to applanate pileus, a white context discolouring purplish-red on exposure, cheilocystidia devoid of encrustations and a trichoderm-type pileipellis.

Comparison of the ITS (676 bp), LSU (924 bp) and RPB2 (702 bp) sequences of I. rubrobrunnea with the nucleotide sequences of taxa available in GenBank numbers suggests that it has distinct sequences. In a megablast search of the GenBank numbers database using ITS sequence of I. rubrobrunnea, the closest hit was Inocybe species MCA562 (GenBank numbers JQ408785; Identities = 616/668 (92%)) followed by Inocybe species AU43 (GenBank numbers KJ729878; Identities = 605/659 (92%)). An undescribed Inocybe species, Inocybe species AU44 was the closest hit in BLASTn search with LSU (GenBank numbers KJ729906; Identities = 896/925 (97%)) sequence. Inocybe species AU43 (GenBank numbers KJ729935; Identities = 670/702 (95%)) resulted as the closest hit in BLASTn search with RPB2 sequences. But, the details of Inocybe species MCA562, an unnamed Inocybe collection from Japan and Inocybe species AU43 and Inocybe species AU44, another unnamed collection from Australia, are not available for comparison.

The RPB2-based ML phylogeny placed Inocybe rubrobrunnea in the Pseudosperma clade with full support (100% ML). Within this clade, I. rubrobrunnea clustered with Inocybe species AU43 with a significant support (95% ML).

Phylogram generated from maximum likelihood (RAxML) analysis based on RPB2 sequence data matrix for 34 Inocybe species. Sequences of Inocybe species belonging to the Pseudosperma clade used in this study have been selected from a previous analysis of Kropp et al. (2013). Values at nodes indicate bootstrap support. BS values ≥50% are shown. Inocybe luteobrunnea, I. brunneosquamulosa and I. rubrobrunnea are in pink to highlight its phylogenetic position in the tree. The tree is rooted with I. adaequata and I. calamistrata of Inosperma clade.

Inocybe rubrobrunnea (CAL 1307, holotype). a, b Basidiocarp in the field. Scale bars: a, b = 5 mm (photos by K. P. Deepna Latha)

Inocybe rubrobrunnea (CAL 1307, holotype). a Basidiospores. b Basidium. c Cheilocystidia. d Stipitipellis. e Caulocystidia. f Pileipellis. Scale bars: a-c = 10 μm, d, e = 100 μm (photos by K. P. Deepna Latha)