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

MycoBank number: MB 816734 Facesoffungi number: FoF 2177

Etymology: referring to the yellowish-brown pileus.

Holotype: CAL 1260

Basidiocarps small. Pileus 6–14 mm diam., narrowly conical when very young, becoming conico-convex and finally convex with a small umbo; surface brown (6F6/OAC636) on the squamules and yellowish-brown (5D8/OAC775) elsewhere when young, becoming dark brown (6F7/OAC639) at the centre and on the squamules and brownish-orange (5C4, 5C5/OAC806) elsewhere at maturity, with appressed- to slightly recurved, minute squamules on and around the umbo, appressed-fibrillose towards the margin; margin incurved when young, becoming decurved to somewhat straight with age, crenate or somewhat wavy, finely fissile. Lamellae emarginate, subventricose, rarely furcate, close, greyish-orange (5B3, 5B4/OAC793), up to 2 mm wide, with lamellulae of 3 lengths; edges fimbriate, rather whitish. Stipe 13–22 × 2–2.5 mm, central, equal, fistulose; surface initially orange grey (6B2/OAC634), becoming greyish-orange (5B2/OAC675) at maturity, appressed-fibrillose all over, finely pruinose towards the apex; base somewhat bulbous, not marginate-bulbous. Odour and taste not distinctive.

Basidiospores 7–8 (9) × 5–6 (6.5) (7.9±0.7 × 5.9±0.5) µm, Q = 1.2–1.6, Qm = 1.4, smooth, ovoid to amygdaliform, slightly thick-walled, pale yellowish-brown. Basidia 23–34 × 8–10 µm, clavate, thin-walled, hyaline, 4-spored or rarely 2-spored; sterigmata up to 5 µm long. Mature basidia slightly projecting beyond the hymenial surface. Pleurocystidia absent. Lamella-edge sterile with abundant cheilocystidia. Cheilocystidia 17–52 × 9–15 µm, versiform: clavate, inflated clavate, cylindrical or cylindrical with apical constriction, cylindro-flexuous, cylindrical with irregular constriction, narrowly utriform, utriform with a median constriction, ovoid, fusiform, submoniliform or short-pedicellate, often septate, thin- to slightly thick-walled, hyaline. Lamellar trama subregular, composed of both narrow and inflated hyphae; hyphae 3–25 µm wide, thin- to slightly thick-walled, hyaline, at times with faint, hyaline encrustations especially towards the edge of the hymenium. Subhymenium poorly developed. Pileus trama subregular; hyphae 9–28 µm wide, pale yellow, thin- to slightly thick-walled. Pileipellis a cutis often transitioning to a trichoderm towards the centre; hyphae 4–11 µm wide, tangled, slightly thick-walled, with a pale-yellow wall pigment and brown spiral encrustations. Stipitipellis a cutis frequently disrupted with bunches of caulocystidia towards the apex; hyphae 5–12 µm wide, thin-to slightly thick-walled, with a pale-yellow wall pigment and hyaline encrustations, some hyphae with dense, yellowish-brown, amorphous contents towards the base. Caulocystidia 13–74 × 7–13 µm, versiform: clavate, narrowly clavate, moniliform, submoniliform, cylindrico-flexuous, cylindrical with an obtuse apex, utriform with a median constriction, cylindrical or ovoid with a rostrate apex, often septate, thin- to slightly thick-walled, hyaline. Clamp connections observed on all hyphae.

Habitat: scattered among bryophytes, on a mud wall.

Material examined: INDIA, Kerala State, Idukki District, Munnar, on the way to Mattupetti top hill station, 31 August 2013, K. P. Deepna Latha DKP167 (CAL 1260, holotype); GenBank numbers ITS: KX073580; LSU: KX073584; RPB2: KX073588; INDIA, Kerala State, Idukki District, Munnar, on the way to Mattupetti top hill station, 9 November 2013, K. P. Deepna Latha DKP251 (CAL 1260, holotype; CAL 1261, paratype). GenBank numbers ITS: KX073581; LSU: KX073585.

Notes: Inocybe luteobrunnea is characterised by a yellowish-brown pileus with a fibrillose to minutely squamulose surface; a fibrillose stipe with a finely pruinose apex and a bulbous base; smooth, ovoid to amygdaliform basidiospores; a hymenium lacking pleurocystidia; abundant, versiform cheilocystidia; subregular lamellar trama with faint hyaline encrustations; a pileipellis that is a cutis with a transition to a trichoderm towards the centre and a cutis-type stipitipellis frequently disrupted with bunches of caulocystidia confined to the stipe apex. Inocybe palaeotropica E. Turnbull & Watling, a widespread species reported from Singapore, Malaysia, Sabah, Papua New Guinea, Solomon Islands (Horak 1980b) and also recorded from Kerala by Vrinda et al. (1997, as I. umbrina Massee), shares a few characters with I. luteobrunnea such as a similar-shaped pileus, similar-sized basidiospores (7.5–10.5 × 4.5–6 µm), a sterile lamella-edge and caulocystidia on the stipe apex. Inocybe palaeotropica, however, has larger basidiocarps with dissimilar colour and surface features, adnexed lamellae, a fibrillose stipe devoid of apical pruinosity, ovoid to short ellipsoid basidiospores, only 4-spored basidia, clavate to cylindro-clavate cheilocystidia, hyphae of lamellar trama lacking encrustations, a cutis-type pileipellis and smaller, cylindro-clavate caulocystidia. Inocybe luteobrunnea is somewhat similar to I. fuscospinulosa Corner & E. Horak, an Indonesian species (Horak 1980b) and also reported from Sri Lanka (Pegler 1986), in having a somewhat similar-shaped pileus, a fibrillose stipe, almost similar-sized basidiospores (6.5–8 × 4–5 µm), cheilocystidia, a hymenium devoid of pleurocystidia and an almost similar pileipellis structure. However, I. fuscospinulosa differs from I. luteobrunnea owing to its larger basidiocarps with conspicuous, erect, spiny squamules on the pileus, crowded, adnexed, tobacco-brown lamellae, a red-brown tinged stipe with occasional brown squamules and without a distinct bulbous base, ovoid basidiospores, consistently 4-spored basidia, larger, differently-shaped cheilocystidia and a stipitipellis devoid of caulocystidia.

The distinctive status of (CAL 1260: 675 bp; CAL 1261: 674 bp), LSU (CAL 1260: 838 bp; CAL 1261: 746 bp) and RPB2 (CAL 1260: 651 bp) sequences of I. luteobrunnea was confirmed in the BLASTn searches. An unnamed Australian species, Inocybe species AU95 was the closest hit in a megablast search for ITS (GenBank numbers KP636851; Identities = 540/588 (92%)), LSU (GenBank number KP171053; Identities = 831/839 (99%)) and RPB2 (GenBank number KM555145; Identities = 638/651 (98%)) sequences.

The phylogram generated from the Maximum Likelihood (ML) analysis depicts the relative placement of I. luteobrunnea. The ML analysis placed I. luteobrunnea in the Pseudosperma clade with full support (100% ML) based on RPB2 sequence data matrix. Within this clade, I. luteobrunnea clustered with an unnamed Australian species, Inocybe species AU95 (KM555145) with maximum support (100% ML). The macro-morphological and microscopic data of that species are not available for comparison.

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 luteobrunnea (CAL 1260, holotype). a, b Basidiocarp in the field. Scale bars: a, b = 5 mm (photos by K. P. Deepna Latha).

Inocybe luteobrunnea (CAL 1260, holotype). a Basidiospores. b Basidium. c Cheilocystidia. d Caulocystidia. e Pileipellis. Scale bars: a-d = 10 μm, e = 100 μm (photos by K. P. Deepna Latha).