Meripilus crystallinus Y. C. Dai, Chao G. Wang & Yuan Yuan 2025, sp. nov.

Meripilus crystallinus Y. C. Dai, Chao G. Wang & Yuan Yuan, sp. nov. Figs 14, 15 Etymology. Crystallinus (Lat.): refers to the species having hyphoid cystidia with crystals. Diagnosis. Differs from other Meripilus species by resupinate basidiomata with buff yellow, salmon to clay pink pore surface when dry, angular pores of 6–8 per mm, thin-walled and apically encrusted hyphae at the dissepiment edge, broadly ellipsoid to ovoid and slightly thick-walled basidiospores measuring 4.3–5 × 4–4.5 µm. Type. CHINA • Yunnan Province, Weixi County, Laojunshan Nature Reserve, on fallen trunk of Picea, 22 September 2011, Cui 10491 (BJFC 011386, holotype). Description. Basidiomata annual, resupinate, soft to ceraceous, and without odor or taste when fresh, becoming brittle upon drying, up to 10 cm long, 6 cm wide, and 3.2 mm thick at the center. Pore surface buff yellow, salmon to clay pink when dry; sterile margin almost absent; pores angular, 6–8 per mm; dissepiments thin, entire to slightly lacerate. Subiculum very thin to almost absent, up to 0.2 mm thick. Tubes concolorous with pore surface, brittle when dry, up to 3 mm long. Hyphal system monomitic; generative hyphae simple septate, hyaline to yellowish brown, smooth, IKI -, CB +; tissues unchanged in KOH. Subicular hyphae slightly thick-walled with a wide lumen, unbranched, moderately simple septate, slightly flexuous, loosely interwoven, agglutinated, 4–7 µm in diam. Tramal hyphae slightly thick- to thick-walled with a wide lumen, occasionally branched, frequently simple septate, slightly flexuous, subparallel along the tubes, agglutinated, 3–5 µm in diam.; some thin-walled hyphae at the dissepiment edge bearing crystals at the tips and resembling hyphoid cystidia. Hymenial cystidia absent; cystidioles fusoid, thin-walled, smooth, 12–18 × 4–5 µm; basidia barrel-shaped, with four sterigmata and a simple basal septum, 11–12 × 5.5–6 µm; basidioles of similar shape to basidia, but smaller. Basidiospores broadly ellipsoid to ovoid, hyaline, slightly thick-walled, smooth, sometimes with one medium guttule, IKI -, weakly CB +, (4.2 –) 4.3–5 × 4–4.5 µm, L = 4.75 µm, W = 4.15 µm, Q = 1.13–1.15 (n = 60 / 2). Additional specimen examined. CHINA • Yunnan Province, Weixi County, Laojunshan Nature Reserve, on fallen trunk of Picea, 22 September 2011, Cui 10475 (BJFC 011370). Notes. Meripilus crystallinus is similar and related to M. eminens (Y. C. Dai) Rajchenb. & Westph. by having annual and resupinate basidiomata, the absence of a sterile margin, angular and almost the same size pores (7–8 per mm in M. eminens; 6–8 per mm in M. crystallinus, Dai 1998), and almost the same size as basidiospores (4.2–6 × 3.9–5.2 µm in M. eminens; 4.3–5 × 4–4.5 µm in M. crystallinus, Dai 1998). However, M. eminens has thin- to fairly thick-walled tramal hyphae, and thick-walled and apically encrusted hyphoid cystidia penetrating above the hymenial surface (Dai 1998). Meripilus vitreus (Pers.) Rajchenb. & Westph. is phylogenetically related to M. crystallinus (Fig. 4), but M. vitreus has thick-walled hyphoid cystidia with coarse crystals in most specimens, relatively bigger pores (5–6 per mm vs. 6–8 per mm), and thin-walled basidiospores (5–5.5 × 4–4.5 µm vs. 4.3–5 × 4–4.5 µm, Wang et al. 2024). In addition, there are 20 base pair differences in ITS sequences between these two species, which accounts for a 3 % nucleotide difference in the ITS regions. Meripilus crystallinus and M. stillicidiorum (Speg.) Rajchenb. & Westph. share the pinkish buff, buff yellow, salmon to clay pink pore surface, the absence of sterile margin, and almost the same pore size (5–7 per mm in M. stillicidiorum; 6–8 per mm in M. crystallinus, Wang et al. 2024). However, M. stillicidiorum lacks any kind of cystidia, relatively larger basidiospores (5–5.7 × 4–4.8 µm vs. 4.3–5 × 4–4.5 µm, Wang et al. 2024), and so far, is only known from the type locality in Australia. Meripilus revolubilis Westph. & R. M. Silveira and M. robledoi Rajchenb. & Westph. were described with the resupinate basidiomata, white, cream to isabelline pore surface, thick-walled encrusted cystidia, which are similar to M. crystallinus (Westphalen et al. 2025). Phylogenetically, Meripilus crystallinus, M. eminens, M. revolubilis, M. robledoi, and M. vitreus form a distinct joint clade and share similar morphological characters.