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

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Basidiodendron odontoideum Q. Yuan & C. L. Zhao sp. nov. Figs 15, 16, 17 Diagnosis. Basidiodendron odontoideum differs from other species by its soft membranaceous basidiomata, odontioid hymenial surface, short clavate cystidia, and globose to subglobose, smooth basidiospores. Etymology. Odontoideum (Lat.). Referring to the odontioid hymenophore of the type specimen. Type. CHINA • Yunnan Province, Zhaotong, Wumeng Mountain National Nature Reserve, 27°58'N, 104°15'E, elevation 2,154 m asl., on fallen angiosperm branch, leg. C. L. Zhao, 28 Aug. 2023, CLZhao 32441 (SWFC 00032441, holotype). Description. Basidiomata annual, resupinate, closely adnate, soft membranaceous, without odor or taste when fresh, up to 11 cm long, 8 cm wide, and up to 50 µm thick. Hymenial surface odontioid, slightly cream when fresh, turning to cream upon drying. Sterile margin narrow, white, up to 1 mm. Hyphal system monomitic; generative hyphae with clamp connections, colorless, thin-walled, smooth, interwoven, 1–2 µm in diameter, IKI –, CB –; tissues unchanged in KOH. Leptocystidia short clavate, colorless, thin-walled, smooth, 6.5–8.5 × 2–2.5 µm. Hyphidia absent. Basidia ellipsoid to ovoid, longitudinally septate, two- to four-celled, 6.5–8.5 × 4.5–5 µm, involucres well developed, often totally covering basidial cells. Basidioles dominant, similar to basidia in shape, but slightly smaller. Basidiospores globose to subglobose, colorless, thin-walled, smooth, usually with one oil drop, IKI –, CB –, 3–3.5 × 2.5–3.5 µm, L = 3.33 µm, W = 3.05 µm, Q = 1.09–1.11 (n = 60 / 2). Additional specimen examined (Paratype). CHINA • Yunnan Province, Zhaotong, Wumeng Mountain National Nature Reserve, 28°02'N, 104°18'E, elevation 2,260 m asl., on fallen angiosperm branch, leg. C. L. Zhao, 28 Aug. 2023, CLZhao 50721 (SWFC 00050721). Notes. Basidiodendron odontoideum forms a single lineage (100 % ML, 1.00 BPP) and resolves in a sister relationship to B. parile in the phylogenetic inference (Fig. 2). Key characters distinguishing B. parile from B. odontoideum are its waxy basidiomata with a smooth hymenial surface and larger basidiospores (4.7–5.9 × 4.1–5.6 µm vs. 3–3.5 × 2.5–3.5 µm; Spirin et al. 2020). Morphologically, B. odontoideum resembles B. alni, B. mexicanum Spirin & Malysheva, and B. microsporum Spirin, Malysheva & Kotiranta in having globose to subglobose basidiospores. However, B. alni can be separated from B. odontoideum by its smooth hymenial surface and larger basidiospores (4.1–5 × 4.2–5 µm vs. 3–3.5 × 2.5–3.5 µm; Spirin et al. 2020). Basidiodendron mexicanum is distinct from B. odontoideum by its pruinose basidiomata, smooth hymenial surface, and larger basidiospores (5.9–7.3 × 6.1–7.4 µm vs. 3–3.5 × 2.5–3.5 µm; Spirin et al. 2021). Basidiodendron microsporum differs from B. odontoideum by its pruinose-reticulate basidiomata and smooth hymenial surface (Spirin et al. 2020).