Cortinarius mucobrunneus T. S. Li, Y. Zhang & Q. Zhao 2026, sp. nov

Cortinarius mucobrunneus T. S. Li, Y. Zhang & Q. Zhao sp. nov Fig. 2 Chinese name: 黏褐丝膜菌 (nian he si mo jun) Etymology. mucobrunneus refers to the brown pileus with mucus on the surface. Holotype. China • Yunnan Province: Lijiang City, Laojunshan Nature Reserve, at 26.631426°N, 99.719085°E, alt. 3960 m, in Abies forest, 26 Aug. 2018, LJ 1678 (HKAS 149459). Diagnosis. Similar to Cortinarius vanduzerensis in the sticky pileus surface, but differing in the larger basidiospores. Macrostructures. Basidiomata medium-sized. Pileus 40–60 mm diam., conical to campanulate, becoming applanate and umbonate with age; surface viscid, dark brown (7 F 8) to liver brown (8 F 8); margin tile red (7 D 8) to platinum blonde (4 B 3), undulate, translucent radially striate; context 4–5 mm thick at mid-radius, white. Lamellae adnate to adnexed, 3–4 mm broad, moderately crowded, cinnamon (6 D 4) to brown (6 E 7); edge serrate. Stipe 50–80 × 7–12 mm, cylindrical, usually tapering upwards; surface viscid, white, leaving a cinnamon (6 D 5) ring on the upper part of the stipe. Basal mycelium white. Odour not distinctive. Microstructures. Basidiospores [100 / 2 / 2] (13 –) 13.5–16 (– 17) × 8–10 (– 10.5) μm [Q = (1.42) 1.52–1.91 (– 2), Q = 1.66 ± 0.09], elliptical to amygdaliform, cinnamon in KOH, strongly verrucose. Basidia 40–57 × 14–17 μm, clavate, 4 - spored. Lamella trama hyphae 4–16 μm diam., smooth, colourless. Lamellar edges fertile. Pileipellis duplex: epicutis strongly gelatinous, 110–230 μm thick, composed of flat, loosely arranged, long-celled, colourless hyphae 4–10 μm diam.; hypocutis 35–70 μm thick, composed of cylindrical to elliptical, strongly interwoven, colourless hyphae 4–12 μm diam., some hyphae with spiral or spotted encrustations. Stipe hyphae 4–10 μm diam., colourless, smooth. Clamp connections absent. Habitat. Mycorrhizal, gregarious in coniferous forests dominated by Picea spp. and Abies spp. trees. Distribution. Known from the southern Yunnan Province, China. Additional material examined. China • Yunnan Province: Lijiang City, Laojunshan Nature Reserve, at 26.631426°N, 99.719085°E, alt. 3960 m, in Abies forest, 16 Aug. 2017, LJ 981 (HKAS 149456). Notes. Cortinarius mucobrunneus is characterized by its victid basidiomata, dark brown pileus with translucent stripes, cinnamon to brown lamellae, white stipe leaving a cinnamon ring on the upper part, and elliptical to amygdaliform, strongly warty basidiospores. Phylogenetic analysis indicates that C. mucobrunneus is nested in sect. Defibulati and is more closely related to C. mucifluus and C. vanduzerensis (Fig. 1). Morphologically, C. mucobrunneus showcases a dark brown pileus with tile red to platinum blonde margins alongside a white stipe, in contrast to C. vanduzerensis has a chestnut-black pileus with chestnut-brown margins and a light purple to dark lavender stipe (Smith and Trappe 1972). Furthermore, C. mucobrunneus has larger basidiospores [13 –) 13.5–16 (– 17) × 8–10 (– 10.5) μm vs. (11 –) 12–14 (– 15) × 7–8 (– 9) μm] than C. vanduzerensis (Smith and Trappe 1972). Cortinarius mucobrunneus is frequently misidentified as C. mucifluus due to the presence of translucent striations along the margin of the pileus, the pale stipe, and the cinnamon-hued annulus situated on the upper portion of the stipe. Nevertheless, C. mucobrunneus is characterized by a dark brown to liver brown pileus that exhibits broader basidiospores, in contrast to the ochraceous brown pileus of C. mucifluus, which features comparatively narrower basidiospores.