Byssosphaeria chishuiense L. L. Liu & Z. Y. Liu 2025, sp. nov.

Byssosphaeria chishuiense L. L. Liu & Z. Y. Liu sp. nov. Fig. 2 Etymology. Refers to the Chishui River basin, where the holotype was collected. Holotype. GZAAS 20-0374. Description. Saprobic on decaying, submerged wood in freshwater habitats. Sexual morph. Ascomata superficial, gregarious, unilocular, globose to subglobose, 220–390 μm high, 520–740 μm diam., broadly or narrowly conical, black, carbonaceous, roughened and irregular, ostiolate. Ostiole single, central, papillate. Peridium 33–58 μm wide at sides, brown, thick-walled, of textura angularis, comprising a mixture of host and fungal cells. Hamathecium 2.5–3.5 μm wide, composed of dense, trabeculate, distinctly septate, anastomosing, pseudoparaphyses, embedded in a hyaline gelatinous matrix. Asci 111–163 (– 220) × 14–24.5 μm (x ̄ = 145 × 19 μm, n = 20), 8 - spored, bitunicate, fissitunicate, cylindrical clavate, short pedicel, apically round, with an ocular chamber. Ascospores overlapping, 1–2 - seriate, fusiform, hyaline, 1 - septate, constricted at the central septum, lower cell wider and longer than upper cell, 41.5–51.5 × 7–9 μm (x ̄ = 45.5 × 8 μm, n = 30), tapering to pointed apices, mostly straight, surrounded by a thick distinctive sheath, 4–6.3 μm wide (in water-mounted slide), drawn out at the ends, smooth-walled. Asexual morph. Undetermined. Cultural characteristics. Conidia germinated on WA, and germ tubes were produced from both ends within 12 h. Colonies on PDA overgrew the culture dish after 3 weeks at 25 ° C in dark, circular, mycelia dense in the middle and sparse in the edge, white from above, pale yellow from reverse. Material examined. China • Guizhou Province, Chishui River basin, near 28°25'N, 106°0'E, at 500 m altitude, saprobic on submerged decaying wood in a freshwater stream, July 2019, L. L. Liu, CS 1-13 (GZAAS 20-0374, holotype); • ex-type living culture ACCC 35242. Taxonomic notes. Morphologically, B. chishuiense is characterized by superficial ascomata with bright yellow or orange flat apices around the ostiole and hyaline ascospores (Fig. 2). These characteristics are consistent with the generic concept of Byssosphaeria (Barr 1990). Phylogenetic analyses of the combined LSU, SSU, ITS, and tef- 1 α sequence data showed that B. chishuiense (ACCC 35242) was sister to B. villosa (GKM 204 N), and they reside within the Melanommataceae (Fig. 1). Although B. chishuiense and B. villosa have the same-sized asci (140–200 × 17–25 vs. 140–200 × 17–25 μm), B. chishuiense can be distinguished from B. villosa in having larger ascospores (41.5–51.5 × 7–9 vs. 30–40 × 8–12 μm) and ascomata (520–740 vs. 430–500 μm diam.) and the absence of appendages (Samuels and Müller 1978). The main morphological differences between Byssosphaeria spp. are detailed in Table 2. Additionally, comparing 828 nucleotides across the LSU gene region between B. chishuiense and B. villosa revealed 29 bp (3.50 %) differences. Our molecular data also support that B. chishuiense and B. villosa are phylogenetically distinct (Fig. 1).