Marasmius unicuspidatus T. Bau & W. N. Hou 2026, sp. nov.

Marasmius unicuspidatus T. Bau & W. N. Hou sp. nov. Figs 4 F – I, 8 Diagnosis. It is characterized by a pileus surface with faint longitudinal grooves, emarginate to sinuate lamellae, and mostly unbranched setiform cheilocystidia and pleurocystidia. Etymology. “ unicuspidatus ” refers to the setiform cheilocystidia and pleurocystidia of this species, which are unbranched at the apex, with most bearing only a single pointed tip. Description. Basidiomata small. Pileus 0.6–0.8 cm diam., convex; surface pale orange-yellow (RAL 1017), orange-brown (RAL 8023) at the disc, smooth, with indistinct, shallow longitudinal grooves; margin entire; apex flat. Context thin, greyish-white (RAL 1013); odor indistinct. Lamellae emarginate to sinuate, sparse, unequal, narrow, 1–1.5 mm wide, L = 10, I = 1–2, cream-colored, densely covered with ochre (RAL 1024) tomentum; margin wavy. Stipe 4.5 cm long, 0.5–1 mm thick, cylindrical, slightly thicker at apex; apex greyish-white (RAL 9002), middle pale orange-brown (RAL 8023) to ochre-brown (RAL 8001), base deep reddish-brown (RAL 8012); hollow; surface smooth; base attached to habitat with a small amount of cream-colored (RAL 9001) mycelium. Basidiospores (5.6) 6.01–8.8 (8.9) × (3.1) 3.4–5.3 (5.3) μm, Q = (1.39) 1.45–1.95 (2.07) [1.69 ± 0.16], ovoid, smooth, thin-walled, hyaline, inamyloid. Basidia 18–25 × 4.8–6.3 μm, clavate, thin-walled, hyaline, 2 - sterigmate; sterigmata 1.5–2.9 μm long. Basidioles 18–33 × 4.6–8.9 μm, clavate, smooth, thin-walled, hyaline. Cheilocystidia 28–43 × 3.2–6.3 μm, setiform, mostly unbranched, with a few bearing two or three apical branches, thick-walled, pale brown in 5 % KOH. Pleurocystidia 19–60 × 5.1–11 μm, setiform, thick-walled, pale brown in 5 % KOH. Lamellar trama irregular; hyphae 3.4–5.8 μm wide, thin-walled, hyaline, dextrinoid. Pileipellis hymeniform, composed of Siccus - type, 13–25 × 4.6–9.3 μm; main body clavate to elongate-cylindrical, apex bearing 3–17 small spines; spines 5.6–12 μm long, weakly dextrinoid. Pileus trama composed of interwoven, thin-walled, smooth, hyaline, dextrinoid hyphae 3.9–6.3 μm wide. Stipitipellis composed of parallel, slightly thick-walled, smooth hyphae 3.3–5.6 μm wide, pale yellowish-brown in 5 % KOH. Clamp connections present in all tissues. Typus. CHINA • Heilongjiang Province, Harbin City, Shangzhi City, Mao’er Mountain, on decaying leaves of broad-leaved trees, 6 July 2025, 45°18'47"N, 127°33'21"E, alt. 302 m, W. N. Hou, FJAU 69384 (H 25070602), holotype!. Additional materials examined. CHINA • Jilin Province, Changchun City, Jingyuetan National Forest Park, on decaying leaves of broad-leaved trees, 20 July 2025, 43°46'56"N, 125°26'57"E, alt. 208 m, X. Y. Zhou, FJAU 69385 (Y 2572031). Notes. This species, together with Ma. cohaerens (Pers.) Cooke & Quél., belongs to Marasmius subg. Globulares sect. Globulares subsect. Globulares ser. Cohaerentes. Species within this series show a typical temperate distribution pattern. The series includes Ma. cohaerens, Ma. cohaerens var. lachnophyllus (Berk.) Gilliam, and Ma. cohaerens var. mandshuricus Kiyashko, E. F. Malysheva & Antonín. Ma. cohaerens var. lachnophyllus differs from the typical by the absence of caulocystidia, while Ma. cohaerens var. mandshuricus is recognized by its larger pleurocystidia (Kiyashko et al. 2014). Ma. cohaerens, a species widely distributed across China, differs from Ma. unicuspidatus in having a distinctly umbonate pileus with a tomentose surface, abundant setiform pileocystidia, and cheilocystidia and pleurocystidia that are mostly, and often profusely, branched. In contrast, Ma. unicuspidatus has a flat pileus apex and a smooth surface, lacks setiform pileocystidia, and possesses setiform cheilocystidia and pleurocystidia that are almost entirely unbranched at the apex (Cooke and Quélet 1878; Deng 2012). Ma. delectans Morgan is similar in overall macromorphology and basidiospore size, but differs through its predominantly North American distribution, brown-edged lamellae, and setiform cheilocystidia and pleurocystidia that are usually constricted one or more times toward the apex (Gilliam 1976). Furthermore, Ma. unicuspidatus differs from Ma. crinipes, another member of sect. Globulares widely distributed across the Northeast China Ecological Region. Specifically, Ma. crinipes possesses free or shortly adnexed lamellae that occasionally form a false collarium, together with clavate basidiospores (20–27 × 3.5–5.0 µm, Q = 5.0–6.1) (Antonín et al. 2012 b).