Mystinarius ochrobrunneus Ammirati, Halling, Niskanen & Liimat., sp. nov.

Index Fungorum number: IF 900309; Mycobank number: MB 900309; Facesoffungi number: FoF 14866; Figs. 1e, 2e

Etymology –  Named for the general coloration of the basidiomes.

Holotype –  CR 4064459.

Pileus 2.5–4 cm in diam, campanulate to obtuseumbonate, rarely plano-umbonate, margin often irregular, 1/3–1/2 pellucid striate, orange yellow brown to orange brown or reddish brown, margin ochraceous brown to light ochraceous tawny with darker brown striations or more orange ochraceous brown, edge sometimes very pale, viscid. Lamellae crowded to subcrowded, adnexed, bright ochraceous brown, pallid to whitish in places. Stipe 7–9 cm long, 0.4–0.6 cm thick at the apex, up to 1.3 cm at the base, clavate-bulbous, at first white then yellowish, colour often watery, viscid at mid-stipe when young. Context to 3–4 mm on disc, very thin over lamellae, watery and±concolorous (watery brown), in stipe hollow, cortex white to watery white, in hollow ochraceous to pale watery yellowish. Universal veil white, forming thin patches on the stipe. Mycelium white. Odour fungoid. Taste of gluten and context bitter. Basidiospores 8–9×5–5.5 µm, amygdaloid to somewhat ellipsoid, finely verrucose. ITS sequence (GenBank ON843422, ex holotype) distinct from M. lustrabilis with 98% similarity.

Habitat and distribution – In Quercus spp. forests and so far known from Costa Rica.

Material examined – Costa Rica, San José, Pérez Zeledón, Paramo, R.F. Los Santos, San Gerardo de Dota, Albergue de Montaña Savegre, 2200–2500 m, Quercus spp. gregarious in deep leaf litter, 7 June 2004, J. F. Ammirati, 4064459 (holotype in CR; isotypes in NY & K).

GenBank number – ITS=ON843422.

Notes – Mystinarius ochrobrunneus is a rather small and fragile species with bitter taste, viscid orange brown pileus, white, somewhat viscid stipe when young, and amygdaloid to somewhat ellipsoid basidiospores. The sister species M. lustrabilis occurs in Europe. Morphologically the species also resembles those of Thaxterogaster sect. Vibratiles.

Figure 1 – Basidiomes of the species of the genera Cortinarius, Hygronarius and Mystinarius. a Cortinarius flaureifolius (K-M 001434094, holotype). b Cortinarius floridaensis (K-M 001434095, holotype). c Cortinarius subiodes (K-M 001434108, holotype). d Hygronarius californicus (K-M 001434114, holotype). e Mystinarius ochrobrunneus (CR 4064459, holotype). Photographs: a Matthew E. Smith, b–d Kare Liimatainen, e Joseph F Ammirati

Figure 2 – Basidiomes of the species of the genera Cortinarius, Hygronarius and Mystinarius. a Cortinarius flaureifolius (K-M 001434094, holotype). b Cortinarius floridaensis (K-M 001434095, holotype). c Cortinarius subiodes (K-M 001434108, holotype). d Hygronarius californicus (K-M 001434114, holotype). e Mystinarius ochrobrunneus (CR 4064459, holotype). Drawings: Tuula Niskanen. Scale bars: 10 µm