Xenosporidesmium caohaiense L. L. Liu & Z. Y. Liu 2025, sp. nov.

Xenosporidesmium caohaiense L. L. Liu & Z. Y. Liu sp. nov. Fig. 2 Etymology. The epithet “caohaiense” refers to the type location, Caohai National Nature Reserve. Holotype. HKAS 150269 Description. Saprobic on decaying submerged wood in freshwater habitats. Sexual morph: Unknown. Asexual morph: Hyphomycetous. Colonies on natural substrate effuse, hairy, dark brown, scattered or in small groups, velvety. Mycelium mostly immersed, composed of pale to brown, branched, septate, smooth hyphae. Conidiophores macronematous, mononematous, erect, solitary, straight or slightly flexuous, unbranched, cylindrical, dark brown, 1–3 - septate, 25.5–50 × 3.5–6 μm (x ̄ = 37 × 4.5 μm, n = 20). Conidiogenous cells monoblastic, integrated, terminal, cylindrical or lageniform, pale brown, (6 –) 9–14.5 × 2.5–5.5 μm (x ̄ = 11 × 4 μm, n = 20). Conidia 35–51 × 7.5–11 μm (x ̄ = 42 × 9 μm, n = 20), acrogenous, solitary, obclavate, pale brown, straight or slightly flexuous, apically rostrate, hyaline to pale brown, often with a mucilaginous sheath, truncate at the base, 8–13 - distoseptate, guttulate, smooth-walled, thin-walled. Culture characteristics. Conidia germinating on PDA medium within 12 h. Germ tubes produced from the apex. Colonies on PDA medium reaching 20 mm diam. after 3 weeks at 25 ° C, circular, flat, centrally umbonate, with velvety, white to pale yellow mycelium on the surface; in reverse pale yellow with entire margin. Material examined. China • Guizhou Province, Bijie City, Weining District, Caohai National Nature Reserve, on decaying wood submerged in a freshwater lake, 4 October 2018, L. L. Liu, 18 C-69 (HKAS 150269, holotype; GZAAS 20-0429, isotype), ex-type cultures GZCC 19-0534; China • Guizhou Province, Zunyi City, Chishui District, on decaying wood submerged in a freshwater stream, 16 July 2019, J. Yang, CS 2-6-1 (HKAS 150268), living cultures GZCC 19-0533. Notes. Xenosporidesmium caohaiense forms a distinct lineage and clusters within the Xenosporidesmium clade by high support (ML-BS = 100 %, BYPP = 1) in the phylogenetic tree, indicating a close relationship with other Xenosporidesmium. The morphological differences with other Xenosporidesmium species are shown in Table 2. Xenosporidesmium filiforme is distinguished from other Xenosporidesmium species by possessing an apical appendage. Xenosporidesmium caohaiense can be differentiated from all other species (except X. olivaceoconidium) based on the dimensions of its conidiophores, conidiogenous cells, and conidia. Although X. caohaiense and X. olivaceoconidium exhibit highly similar morphological characteristics, they are phylogenetically distant in the tree. Additionally, there are 43 bp differences (313 bp, without gaps) in the ITS region between these two species. Therefore, we introduce Xenosporidesmium caohaiense as a novel species here.