Pseudohydnum macroumbrosum T. J. Yu & L. P. Tang 2026, sp. nov.

Pseudohydnum macroumbrosum T. J. Yu & L. P. Tang sp. nov. Fig. 6 Chinese name. 大果暗色刺银耳. Diagnosis. Similar to and phylogenetically close to P. umbrosum, but differs in its significantly larger and thicker pileus, well-developed stipe, and more rounded basidiospores (8.3–10.0 × 7.3–8.7 μm). Holotype. China • Yunnan Province, Shangri-la City (香格里拉市), near the Yijia Village (彝族村), 27°23'07"N, 100°06'23"E, elev. 3,130 m, on decaying Pinus armandii wood, 26 August 2020, leg. W. H. Zhang (holotype, MHKMU ZWH 537). Etymology. From Greek macro - (large) and Latin umbrosum (dark-colored), referring to its phylogenetic and morphological affinity to P. umbrosum combined with its distinctly larger basidiomata. Description. Basidiomata large-sized, gelatinous when fresh, pileate, laterally stipitate, gregarious or imbricate (often confluent at the base). Pileus up to 110 mm in widest diameter and 10 mm thick, auriform to semicircular or flabellate; pileal surface papillate to minutely velutinous or strigose, pale brown (4 B 3) to pale yellowish brown (3 B 2) or olive brown (3 D 4), translucent when wet; margin sharp to slightly blunt, entire, rarely undulating, fertile. Hymenophore hydnoid; spines sharp-tipped, 1–3 mm long, 2–4 per mm, white (1 A 1). Stipe 30–60 mm long, 20–40 mm in diam., lateral, white (1 A 1) to watery-grayish (1 B 1), irregular, typically tapering upward from a bulbous base, somewhat compressed, translucent; surface covered with short spines. Context gelatinous, translucent, unchanging. Odor and taste mild. Basidiospores [60 / 2 / 2] (8.2 –) 8.3–10.0 (– 10.3) × (7.0 –) 7.3–8.7 (– 9.2) μm, Q = (1.02 –) 1.05–1.23 (– 1.25), Qm = 1.15 ± 0.05, subglobose to broadly ellipsoid, hyaline, smooth, thin-walled, nonamyloid, with a small apiculus, frequently germinating by repetition or by germ tubes. Basidia 13–16 × 10–16 μm, longitudinally cruciate-septate, 4 - spored, arranged in a dense palisade extending to the spine apices; sterigmata up to 26 × 2–6 μm. Hyphidia 2–4.5 μm wide, common, branched, with simple septa or clamp connections. Hyphal system monomitic, generative hyphae with clamp connections. Pileipellis composed of subparallel or ascending hyphae, 2–8 μm in diam., slightly inflated, thin- or slightly thick-walled, hyaline to brownish. Contextual hyphae 2-9 μm in diam., frequently branched, interwoven, thin- to slightly thick-walled, hyaline. Subhymenial hyphae hyaline, thin-walled, interwoven or anastomosing, 2–7 μm in diam., occasionally inflated up to 17 μm. Ecology and distribution. Growing on decayed coniferous wood (Pinus armandii). Currently known only from Yunnan, southwestern China. Other specimens examined. China • Yunnan Province, Shangri-la City (香格里拉市), near Yijia Village (彝族村), 27°23'07"N, 100°06'23"E, elev. 3,130 m, on decaying Pinus armandii wood, 26 August 2020, leg. W. H. Zhang (MHKMU ZWH 537-1); • ibid., 27°23'10"N, 100°06'29"E, elev. 3,180 m, on decaying Pinus armandii wood, 30 July 2021, leg. W. H. Zhang (paratype, MHKMU ZWH 661). Comments. Pseudohydnum macroumbrosum is distinguished by its imbricate, often confluent basidiomata, exceptionally large pileus (up to 110 mm in widest diameter), well-developed stipe, and subglobose to broadly ellipsoid basidiospores (8.3–10.0 × 7.3–8.7 μm). Morphologically, it superficially resembles P. brunneovelutinum, P. motuoense, and P. totarae (Lloyd) J. A. Cooper, all of which have significantly smaller basidiomata and basidiospores. However, P. brunneovelutinum differs in its small-sized basidiomata with a short to rudimentary stipe base, sparse spines, smaller basidiospores (5.9–6.8 × 5.2–6.3 μm), and its occurrence on decayed angiosperm wood (Coelho-Nascimento et al. 2024). Pseudohydnum motuoense differs in its small basidiomata, slender stipe often expanding at the base, and much smaller basidiospores (5.5–6.8 × 4.6–6.0 μm) (Lei et al. 2025). Pseudohydnum totarae differs in having smaller, grayish brown to reddish brown pileus, smaller basidiospores (5.5–6.5 × 4.8–5.7 µm), and smaller basidia (Zhou et al. 2022). Phylogenetically, P. macroumbrosum is sister to P. umbrosum, but the latter has nearly sessile basidiomata, a much smaller pileus (≤ 20 mm), and narrower basidiospores (7.6–9.8 × 6.0–7.1 μm) (Spirin et al. 2023).