Marasmius daqinggouensis T. Bau & H. Y. Bao 2026, sp. nov.

Marasmius daqinggouensis T. Bau & H. Y. Bao sp. nov. Figs 5 F, 5 K, 10 Diagnosis. It differs from Ma. castanocephalus J. S. Oliveira in possessing more slender basidiospores and pleurocystidia with apices that are constricted or bear cylindrical projections. Etymology. “ daqinggouensis ” refers to Daqinggou National Nature Reserve, where the type specimen was collected. Description. Basidiomata small. Pileus 0.2–0.8 cm diam., initially hemispherical to convex, becoming plano-convex at maturity, center slightly raised; surface pale reddish-brown (RAL 3012), smooth, soft, fragile, with very shallow longitudinal grooves; margin white (RAL 9003), initially involute, later slightly recurved. Context white (RAL 9003), very thin; odor indistinct. Lamellae free, sparse, equal, L = 12, white (RAL 9003) to cream (RAL 9001), sometimes tinged pale reddish-brown (RAL 3012). Stipe 1.4–3.6 cm long, less than 1 mm thick, filiform, nearly equal; apex grayish-white (RAL 9002), translucent, middle gray (RAL 7004), base olive-brown (RAL 8008) to reddish-brown (RAL 8012), darkening with maturity; surface smooth; base with white (RAL 9003) mycelium attached to habitat. Basidiospores (11) 12–15 (16) × (2) 2.4–3.5 (3.7) µm, Q = (3.78) 4.09–6.03 (6.67) [4.90 ± 0.61], subfusiform, apex acute, base rounded, smooth, thin-walled, hyaline, inamyloid. Basidia 23–29 × 5.3–7.5 µm, elongate-clavate, thin-walled, hyaline, 4 - (rarely 2 -) sterigmate; sterigmata 2.2–5.8 µm long. Basidioles 20–26 × 4.8–6.6 µm, fusiform to clavate, thin-walled. Cheilocystidia Siccus - type, main body 6.4–10 × 3.2–7.7 µm, elongate-cylindrical; apex bearing 6–25 small spines, spines 2.3–3.9 µm long, pale brown in 5 % KOH. Pleurocystidia 20–35 × 6–9.2 µm, main body narrowly cylindrical, with the apex constricted or bearing cylindrical projections, 3.1–8.3 µm long; thin-walled, refractive. Lamellar trama interwoven; hyphae 2.6–4.5 µm wide, thin-walled, hyaline, dextrinoid. Pileipellis hymeniform, composed of Siccus - type, main body 8–15 × 3.4–6.7 µm, subcylindrical to clavate; apex bearing 6–14 small spines, which are borne directly on the apical surface when projections or branches are absent, or on the 1–3 projections / branches when these are present; spines 1.6–8.5 µm long. Pileus trama composed of interwoven, weakly dextrinoid hyphae 2.4–3.8 µm wide. Stipitipellis composed of parallel, slightly thick-walled hyphae 3.8–5 µm wide. Typus. CHINA • Inner Mongolia Autonomous Region, Tongliao City, Horqin Left Wing Rear Banner, Daqinggou National Nature Reserve, on rotten wood of broad-leaved trees, 16 July 2023, 42°48'09"N, 122°10'23"E, alt. 220 m, T. Bau & H. Y. Bao, FJAU 69391 (H 2307121), holotype!. Additional materials examined. CHINA • Inner Mongolia Autonomous Region, Tongliao City, Horqin Left Wing Rear Banner, Daqinggou National Nature Reserve, 16 July 2023, 42°48'08"N, 122°10'22"E, alt. 223 m, on rotten wood of broad-leaved trees, T. Bau & W. N. Hou, FJAU 69393 (H 2307122). • Tongliao City, Horqin Left Wing Rear Banner, Daqinggou National Nature Reserve, on litter in broad-leaved forests, 42°48'03"N, 122°10'32"E, alt. 218 m, 16 July 2023, T. Bau & X. Y. Zhou, FJAU 69392 (Y 2371637). Notes. It is assigned to ser. Haematocephali based on its narrowly cylindrical pleurocystidia with short cylindrical projections. Historically, numerous specimens of this series collected worldwide were identified as Ma. haematocephalus (Mont.) Fr. Recent studies have confirmed that Ma. haematocephalus sensu lato is not a single pantropical species, but a species complex consisting of several morphologically similar taxa (Oliveira et al. 2022). Within this complex, Ma. haematocephalus s. s. appears to be restricted to the Neotropics, while its closely related taxa are distributed in tropical Africa and the Indo-Malayan region. With its unique geographic location and extensive climatic gradient spanning tropical to temperate zones, China serves as a key region for exploring the diversity, distribution patterns, and evolutionary history of this species complex (Li et al. 2015). To date, only two species within this group have been recorded in China: Ma. haematocephalus and Ma. asiaticus Mešić & Tkalčec. No verified records of species in this group have yet been documented from the Northeast China Ecological Region. Ma. haematocephalus is characterized by a purplish-red pileus with a flat center and a distinctly deeply sulcate surface, as well as cheilocystidia with clavate to obpyriform main bodies (Oliveira et al. 2022). In comparison, Ma. daqinggouensis has a pale reddish-brown pileus with extremely shallow striations or sulcations, and cheilocystidia with elongate-cylindrical main bodies. Ma. asiaticus is easily confused with Ma. daqinggouensis due to their similar pileus color. However, Ma. asiaticus produces elongate lacrymoid basidiospores, measuring 18.5–23 × 3.5–5 µm, (Qm = 5.5 ± 0.7), and pleurocystidia with fusoid to clavate main bodies. In contrast, Ma. daqinggouensis has subfusiform basidiospores measuring 13–14 × 2.7–2.9 µm and pleurocystidia with generally slender cylindrical main bodies (Tan et al. 2009). Ma. fulvoferrugineus Gilliam represents another morphologically similar species, but it can be differentiated by its yellowish-brown pileus with a broad central depression or truncation, a farinaceous odor, and longer basidiospores (Fries 1836). The phylogenetic tree reconstructed in this study indicates that Ma. daqinggouensis is most closely related to Ma. aff. pallescens. Ma. aff. pallescens, however, has a ruby-red pileus, a pale ruby interlamellar hymenium, and pleurocystidia that typically lack apical projections and constrictions. Moreover, when projections are present, they are mostly capitate (Oliveira et al. 2022). In addition, Ma. daqinggouensis has pleurocystidia with apices that are constricted or possess cylindrical projections. Ma. crinipes differs from Ma. daqinggouensis in having clavate basidiospores (20–27 × 3.5–5.0 μm, Q = 5.0–6.1) and fusiform, broadly cylindrical, or clavate pleurocystidia, with rostrate projections or small apical warts and refractive cytoplasmic contents (Antonín et al. 2012 b). In general, Ma. castanocephalus J. S. Oliveira is mainly characterized by a buff brown to brownish beige pileus, such that it can be readily distinguishable from Ma. daqinggouensis in the field (Oliveira et al. 2022).