Hydnum robustum Y. H. Xu, Y. F. Sun & B. K. Cui 2026, sp. nov.

Hydnum robustum Y. H. Xu, Y. F. Sun & B. K. Cui sp. nov. Figs 2 c, d, 4 Etymology. Robustum (Lat.), refers to the robust basidiomata. Diagnosis. Characterized by its robust basidiomata and narrow hyphae on pileipellis (2.5–4.5 µm wide). Type. CHINA. Yunnan Province, Lanping County, Luogujing Nature Reserve, alt. ca. 1900 m, 13 Aug. 2023, Yi-Fei Sun leg., on ground of Pinus forest, Cui 22893 (BJFC, holotype). Description. Basidiomata gregarious, robust, 16–30 mm high, fleshy when fresh, becoming ceraceous and cocky upon drying. Pilei up to 35 mm wide, irregularly round or semicircular, convex to plano-convex when young, infundibuliform when old, shallowly depressed in the center; surface glabrous, azonate, smooth to irregularly bumpy; white to cream (4 A 2), tinged pale yellow (4 A 2–4 A 4) when fresh; turning to orange-brown to reddish brown (7 E 7–8 E 7) when dry. Pileus margin thick, entire, strongly decurved, flatten, concolorous with pileus surface. Context 1–2 mm thick, white to cream white (4 A 2). Hymenophore hydnoid, spines subdecurrent, crowded, 3–4 spines / mm 2 when fresh, evenly distributed, subulate, acute, solitary, up to 2.5 mm long and up to 0.3 mm diam; surface white to yellowish white (4 A 2) when fresh, light brown (6 D 7 / 6 D 8) when dry. Stipes central, robust, up to 25 mm long, 5–15 mm wide, subcylindrical, solid, glabrous, concolorous with spines surface; unchanging when handled; stipe base enlarged and covered with a small amount of white basal mycelium. Odor mild and fruity. Basidiospores subglobose to broadly ellipsoid or ovoid, hyaline, thin-walled, smooth, some with granular contents, IKI –, (3.8 –) 4.1–5.2 (– 5.8) × (3 –) 3.2–4.6 (– 4.9) μm, av. 4.62 ± 0.33 × 3.94 ± 0.38, Q = 1.01–1.37 (n = 60 / 2), Qm = 1.18 ± 0.09. Under SEM, the basidiospores smooth without any ornamentation, each bearing a distinct hilar appendix at the attachment point. Basidia subcylindrical or subclavate to clavate, (20 –) 22–30 (– 33) × (3 –) 4–6.5 μm, usually contains hyaline oily droplets; sterigmata 2–5, 2–5 μm long, 1–1.5 μm wide at base, slightly curving. Basidioles numerous, subcylindrical to subclavate, enlarge at apex, smaller or the same size with basidia, frequently covered with granular substance at the apex. Cystidia absent. Hyphae of spines 2.5–4.5 μm, filamentous, hyaline to pale yellow, thin-walled, apex cylindrical, interwoven, frequently branched, pale yellow in KOH. Pileipellis a mixocutis, hyaline to pale yellow, composed of hyphae 2.5–4.5 µm wide, thin to slightly thick-walled, cylindrical to irregular, slightly inflated at apex. Stipitipellis composed of subcylindrical hyphae, slightly thick-walled, interwoven, 1.5–3 μm wide, yellowish brown, sometimes containing yellowish cytoplasmic pigment. Clamp connections present. Additional materials examined. CHINA. Yunnan Province, Lanping County, Luogujing, alt. ca. 1900 m, 13 Aug. 2023, Yi-Fei Sun leg., on ground of Pinus forest, Cui 22901 (BJFC). Yunnan Province, Lanping County, Luogujing, 13 Aug. 2023, Yi-Fei Sun leg., on ground of Pinus forest, Cui 22904 (BJFC). Yunnan Province, Lanping County, Luogujing, alt. ca. 1900 m, 13 Aug. 2023, Yi-Fei Sun leg., on ground of Pinus forest, Cui 22905 (BJFC). Yunnan Province, Lijiang City, Yulong County, Jiuhe, alt. ca. 2400 m, 1 September 2020, Ming Zhang leg., on ground of mixed forests mainly dominated by Fagaceae and Pinus trees, GDGM 83047. Hubei Province, Huanggang City, Luotian, alt. ca. 800 m, 22 October 2023, Xiaomei Peng leg., on ground of mixed forests mainly dominated by Fagaceae and Pinus trees, GDGM 93020. Distribution. Known only from China. Notes. The specimens numbered as GDGM 83047, GDGM 93020 and HKAS 57714 collected from southern subtropical China were firstly recognized as Hydnum pinicola R. Sugaw. & N. Endo, which is originally described from Japan, having whitish to cream basidiomata, pale yellow or pale orange spines, and relatively smaller basidiospores (4.5–5.5 × 4–5 µm; Sugawara et al. 2022). However, the addition of our new specimens revealed that the material from China formed a separate lineage with strong support in the multi-gene phylogenetic tree (87 % in ML bootstrap, 0.99 BPP). Further morphological study revealed that H. robustum has a wider stipe (up to 25 mm) combined with a lower basidioma (16–30 mm) and shorter spines (up to 3 mm), resulting in a robust appearance. Moreover, the pileipellis and stipitipellis of H. robustum show a broader range of hyphal diameters (pileipellis 2–17 µm, stipitipellis 2–12 µm).