Meripilus albomarginatus Y. C. Dai, Xin Zhang, Chao G. Wang & Yuan Yuan 2025, sp. nov.

Meripilus albomarginatus Y. C. Dai, Xin Zhang, Chao G. Wang & Yuan Yuan sp. nov. Figs 12, 13 Etymology. Albomarginatus (Lat.): refers to the species having a white pileal margin when fresh. Diagnosis. Differs from other Meripilus species by effused-reflexed to pileate basidiomata with buff yellow to cinnamon buff and concentrically zonate-sulcate pileal surface when dry, thick-walled and apically encrusted hyphoid cystidia, subglobose basidiospores measuring 5.2–6.2 × 4.6–5.7 µm. Type. CHINA • Yunnan Province, Honghe, Pingbian County, Daweishan National Forest Park, on fallen angiosperm trunk, 26 June 2019, Dai 19796 (BJFC 031471, holotype). Description. Basidiomata annual, effused-reflexed to pileate, imbricate, soft corky, and without odor or taste when fresh, becoming hard corky upon drying, up to 3 cm long and 2.5 cm wide when resupinate; pileus flabelliform, projecting up to 2 cm, 3.5 cm wide, and 1.6 mm thick at the base. Pileal surface orange-yellow to yellow-brown when fresh, becoming buff yellow to cinnamon buff, velutinate, concentrically zonate, and radially sulcate upon drying; margin sharp, thinning out, white when fresh, buff yellow and slightly curved when dry. Pore surface cream to pinkish buff when fresh, unchanged after bruising, clay buff to grayish brown when dry; sterile margin distinct, thinning out, white when fresh, cream to buff when dry; pores angular, 7–8 per mm; dissepiments thin, entire to slightly lacerate. Subiculum buff yellow, soft corky, up to 0.6 mm thick. Tubes concolorous with pore surface, corky when dry, up to 1 mm long. Hyphal system monomitic; generative hyphae simple septate, hyaline, smooth, IKI -, CB +; tissues unchanged in KOH. Contextual hyphae distinctly thick-walled to almost solid, unbranched, straight, loosely interwoven, 5–9 µm in diam. Tramal hyphae distinctly thick-walled with a median lumen, unbranched, slightly flexuous, subparallel along the tubes, agglutinated, 4–8 µm in diam. Hyphoid cystidia present, arising from tramal hyphae and completely embedded in trama, not projecting from the hymenium and sometimes projecting from the dissepiment edge, thick-walled with swollen tips, apically encrusted, 9–12 µm in diam. at the apex. Hymenial cystidia absent; cystidioles fusoid to mamillate, thin-walled, smooth, 14–17 × 6–6.5 µm; basidia barrel-shaped to somewhat pyriform, with four sterigmata and a simple basal septum, 17–20 × 8–9 µm; basidioles of similar shape to basidia, but smaller. Basidiospores subglobose, hyaline, thin-walled, smooth, with one medium or small guttule, IKI -, CB -, (5 –) 5.2–6.2 (– 6.5) × (4.5 –) 4.6–5.7 (– 6) µm, L = 5.79 µm, W = 5.19 µm, Q = 1.11–1.12 (n = 60 / 2). Additional specimens examined. CHINA • Guangdong Province, Guangzhou, Tianluhu Forest Park, on root of dead bamboo, 20 April 2023, Dai 24711 (BJFC 042265). • Yunnan Province, Yuxi, Shimenxia Forest Park, on dead bamboo, 29 June 2023, Dai 25241 (BJFC 042792). Notes. Meripilus albomarginatus is similar to M. lineatus (Pers.) Westph. & Rajchenb. and M. sublineatus (Y. C. Dai, Yuan Yuan & Chao G. Wang) Westph. & Rajchenb. in morphology by having effused-reflexed to pileate basidiomata with concentrically zonate-sulcate pileal surface, clay buff to gray-brown pore surface when dry, thick-walled and apically encrusted hyphoid cystidia and almost the same size as basidiospores (5–6 µm in M. lineatus; 4.8–5.6 × 4.5–5.2 µm in M. sublineatus; 5.2–6.2 × 4.6–5.7 µm in M. albomarginatus, Ryvarden and Gilbertson 1994; Wang et al. 2024). However, M. lineatus has a pinkish-buff to reddish-brown pileal surface and a bright orange-red pore surface when fresh (Ryvarden and Johansen 1980), and M. sublineatus has a normally azonate pileal surface and ventricose thin-walled hymenial cystidia bearing fine crystals (Wang et al. 2024). Meripilus albomarginatus forms an independent lineage in the Meripilus clade (Fig. 2) and groups with M. lineatus and M. sublineatus in a joint subclade (Fig. 2). However, there are 20 base pair differences in ITS sequences between Meripilus albomarginatus and M. lineatus, which account for a 3 % nucleotide difference in the ITS regions. Four recorded synonyms of Meripilus lineatus (Physisporinus lineatus), viz. Polyporus zonalis Berk. (Sri Lanka), P. pusiolus Ces. (Malaysia), P. punctatus Jungh. (Indonesia), and P. epilinteus Berk. & Broome (Sri Lanka), were originally described from Asia. Polyporus zonalis has a pinkish-buff to reddish-brown upper surface, concolorous margin, and white to dingy livid gray pore surface (Pegler and Waterston 1968); P. punctatus has a cloudy-dirty and pale red pore surface and very small pores (Junghuhn 1838); and P. pusiolus and P. epilinteus have resupinate basidiomata (Berkeley and Broome 1873; Cesati 1879). The above four species are different from Meripilus lineatus, M. sublineatus and M. albomarginatus in morphology.