Rhodocybe luteobrunnea K.N.A. Raj & Manim.

MycoBank: MB 816842 Facesoffungi number: FoF02180

Etymology: The specific epithet refers to the yellowish brown pileus.

Holotype: CAL 1322.

Basidiocarps small, mycenoid. Pileus 5–14 mm diam., initially somewhat conico-convex, becoming convex or broadly convex with a small umbo; surface yellowish brown (5E8/OAC734) on umbo and striations, brownish yellow (5D5, 5D6/OAC743) elsewhere, rather hygrophanous and becoming paler, finely pellucid-striate, glabrous; margin slightly incurved when young, becoming deflexed to almost straight with age, finely wavy. Lamellae sinuate or emarginate with a small decurrent tooth, close, greyish-orange (5B3/OAC574), up to 3 mm wide, with lamellulae of 3 lengths; edge entire to the naked eye, finely torn under a lens, concolourous with the sides. Stipe 7–26 x 1–2 mm, central or slightly eccentric, terete, equal, straight or somewhat flexuous, cartilaginous, solid; surface brownish orange (5C3/OAC730), glabrous to the naked eye, finely appressed fibrillose all over under a lens, finely pruinose towards the apex; base with white mycelial cords. Odour and taste not distinctive. Basidiospores 5–7 x 3–4.5 (5.67 ± 0.54 x 3.97 ± 0.49) um, Q = 1.2–1.7, Qm = 1.44, lacrymoid or pip-shaped, with or without a suprahilar depression in profile view, up to 8, weak angular facets in polar view, finely undulate-pustulate all over, thin-walled. Basidia 16–21 x 5.5–6.5 um, clavate, pale yellow, thin-walled, 4-spored; sterigmata up to 4 um long. Lamella-edge heterogeneous. Cheilocystidia and pleurocystidia present as pseudocystidia. Pseudocystidia 16–30 x 4–6 um, narrowly fusiform, narrowly utriform or cylindrical with an acute apex, with golden yellow or reddish-yellow contents, thin-walled. Lamellar trama subregular; hyphae 4–9 um wide, hyaline or pale yellow, thin-walled. Subhymenium inconspicuous. Pileus trama subregular; hyphae 4–7 um wide, with a pale yellow wall pigment and fine brown spiral encrustations, thin- to slightly thick-walled. Pileipellis an undifferentiated cutis; hyphae 4–7 um wide, with a pale brownish-yellow wall pigment and fine brown encrustations, thin- to slightly thick-walled. Stipitipellis a cutis often disrupted by bunches of flaring out hyphae; hyphae 3–7 um wide, with a pale brownish-yellow wall pigment and fine brown encrustations, thin- to slightly thick-walled. Caulocystidia 10–14 x 2–4 um, versiform: lageniform, cylindrical with a short rostrate apex or flexuous, with a pale brownish-yellow wall pigment, thinwalled. Clamp connections not observed on any hyphae.

Habitat: in small groups, on forest floor, among decaying litter.
Material examined: INDIA, Kerala State, Thrissur District, Peechi, Peechi Forest, 26 July 2010, K. N. Anil Raj AR180 (CAL 1322, holotype).

Notes: Rhodocybe luteobrunnea is distinguished by its yellowish-brown basidiocarps with a finely pellucid-striate
pileus; sinuate or emarginate lamellae; lacrymoid or pip-shaped basidiospores; cylindrical to fusiform pseudocystidia and encrusted pileipellis. A combination of characters such as the centrally stipitate basidiocarps and the presence of pseudocystidia with coloured contents (in KOH) lead the present species to the section Rhodocybe. Rhodocybe perplexa T.J. Baroni & Watling from Malaysia (Baroni and Watling 1999) resembles R. luteobrunnea in having a pileus of similar size and shape, somewhat similar sized basidiospores, presence of pseudocystidia, pileipellis with encrusted hyphae and clampless hyphae (Baroni and Watling 1999). However, R. perplexa has differently coloured basidiocarps, adnate lamellae, shorter stipe, subglobose to ellipsoid basidiospores and larger pseudocystidia. Rhodocybe naucoria Singer, an Argentinean species has similar shaped pileus, similar-sized and somewhat similar-shaped basidiospores and presence of pseudocystidia (Baroni 1981). However, that species differs from the present one in having smaller sized and differently coloured basidiocarps, differently attached lamellae, larger pseudocystidia and presence of birefringent crystals in the hymenial hyphae. Comparison of RPB2 (648 bp), ITS (675 bp) and nLSU (830 bp) sequence data derived from the present Rhodocybe species with the nucleotide sequences of taxa available in GenBank suggests that the sequences are different. In a BLASTn search using the ITS sequence derived from the present species, no close hits with a zero e-value were obtained. Rhodocybe aureicystidiata is the closest hit while conducting a BLASTn search using both nLSU (GenBank AY380407; Identities = 840/852 (99 %)) and RPB2 (GenBank AY337412; Identities = 604/648 (93 %)) sequences. Rhodocybe aureicystidiata Lennox ex T.J. Baroni, a species belonging to the section Rhodocybe (Baroni 1981), shows some similarity to the present species in having rather similar-coloured basidiocarps, encrusted hyphae in the pileipellis and presence of pseudocystidia. However, that species has larger basidiocarps, a depressed pileus which becomes dark red on bruising, inrolled margin, larger and amygdaliform basidiospores, larger and differently shaped pseudocystidia and a different geographical location (Baroni 1981). In the phylogram generated from the ML analysis, Rhodocybe luteobrunnea and R. aureicystidiata, R. pruinosostipitata, R. mellea and Rhodocybe sp. formed a distinct clade with significant support (99 % BS). Within this, R. luteobrunnea and R. aureicystidiata formed another subclade also with significant support (90 % BS).

RPB2-based phylogram generated from maximum likelihood analysis (RAxML) depicting the placement of Rhodocybe indica, R. luteobrunnea and R. griseoaurantia within the genus Rhodocybe. Values at nodes indicate bootstrap support. BS values C50 % are indicated above or below the nodes, new species are in blue bold. The tree is rooted with Tricholoma flavovirens (KC816997) and Catathelasma imperiale (KC816994)

Rhodocybe luteobrunnea (CAL 1322, holotype). Basidiocarps in the field. Scale bar 10 mm (Photo by K.N. Anil Raj)

Rhodocybe luteobrunnea (CAL 1322, holotype). a Basidiospores. b Basidium. c Pseudocystidia. d Pileipellis with encrustations. e Stipitipellis. Scale bars a–e = 10 um (Photos by K.N. Anil Raj)