Basidiodendron fragilissimum Q. Yuan & C. L. Zhao 2026, sp. nov.

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Basidiodendron fragilissimum Q. Yuan & C. L. Zhao sp. nov. Figs 12, 13, 14 Diagnosis. Basidiodendron fragilissimum differs from other species by its olivaceous, smooth hymenial surface, broadly globose to subglobose with a short, often eccentric and asymmetric apiculus basidiospores. Etymology. Fragilissimum (Lat.). Referring to the fragile basidiomata of the type specimen. Type. CHINA • Yunnan Province, Dehong, Longchuan County, Tongbiguan Provincial Reserve, 24°32'N, 97°68'E, elevation 1,807 m asl., on dead bamboo, leg. C. L. Zhao, 3 Oct. 2025, CLZhao 49840 (SWFC 00049840, holotype). Description. Basidiomata annual, resupinate, closely adnate, membranaceous, without odor or taste when fresh, up to 15 cm long, 7 cm wide, and up to 50 µm thick. Hymenial surface smooth, slightly olivaceous when fresh, turning to slightly olivaceous to slightly brown upon drying, fragile. Sterile margin narrow, olivaceous, up to 1 mm. Hyphal system monomitic; generative hyphae with clamp connections, colorless, thin-walled, smooth, interwoven, 1–2.5 µm in diameter, IKI –, CB –; tissues unchanged in KOH. Leptocystidia subclavate, colorless, thin-walled, smooth, 9–15.5 × 2.5–5 µm. Hyphidia arising from generative hyphae, nodulose, frequently branched, colorless, thin-walled, 1–2 µm in diameter. Basidia ellipsoid to ovoid, longitudinally septate, two- to four-celled, 10–13 × 7–9 µm, involucres well developed, often totally covering basidial cells. Basidioles dominant, similar to basidia in shape, but slightly smaller. Basidiospores broadly globose to subglobose with a short, often eccentric and asymmetric apiculus, colorless, thin-walled, smooth, usually with one or more oil drops, IKI –, CB –, (4 –) 4.5–5.5 × 4–5 (– 5.5) µm, L = 5.00 µm, W = 4.74 µm, Q = 1.05–1.06 (n = 60 / 2). Additional specimen examined (Paratype). CHINA • Yunnan Province, Dehong, Longchuan County, Tongbiguan Provincial Reserve, 24°08'N, 97°39'E, elevation 2,218 m asl., on dead bamboo, leg. C. L. Zhao, 3 Oct. 2025, CLZhao 49779 (SWFC 00049779). Notes. Based on the ITS + nrLSU + TEF 1 topology (Fig. 2), Basidiodendron fragilissimum is positioned as sister to B. yunnanense. However, B. yunnanense can be distinguished from B. fragilissimum by its reticulate to porulose, greyish-blue hymenial surface (Duan and Zhao 2022). Morphologically, B. fragilissimum resembles B. inconspicuum and B. iniquum R. L. M. Alvarenga & K. H. Larss. in having a smooth hymenial surface. However, B. inconspicuum is distinct from B. fragilissimum by its whitish or greyish hymenial surface and minutely warted, wider basidiospores (5–6.2 × 5.2–6.5 µm vs. 4.5–5.5 × 4–5 µm; Spirin et al. 2021). Basidiodendron iniquum can be separated from B. fragilissimum by its waxy basidiomata and pale cream-colored or greyish hymenial surface (Spirin et al. 2020).

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.