Morphological and multi-gene phylogenetic analyses reveal Nigrellomyces gen. nov. and one new species in Pleurotheciaceae from China

<i>Nigrellomyces</i> is introduced herein as a new genus to accommodate a novel asexual ascomycete, <i>Nigrellomyces aquaticus</i>, isolated from submerged decaying wood in freshwater habitats in Guizhou Province, China. Phylogenetic analyses based on a combined dataset of ITS, LSU, SSU, and <i>rpb</i>2 sequence data robustly place <i>Nigrellomyces</i> within the family Pleurotheciaceae (Pleurotheciales, Savoryellomycetidae), with strong statistical support. The genus is currently known only from its asexual morph, which is characterized by macronematous, mononematous, erect, unbranched, septate conidiophores; polyblastic, integrated, terminal or intercalary, sympodial proliferations; denticulate conidiogenous cells with swollen apices; and acrogenous, subglobose to globose, ovoid to obovoid, or ellipsoidal, aseptate, guttulate conidia. Morphological comparisons reveal that <i>Nigrellomyces</i> displays a cordana-like conidiogenesis that is distinct from other genera in Pleurotheciaceae, which typically exhibit acrodictys-, helicoön-, monodictys-, or dactylaria-like asexual morphs. This study provides a comprehensive morphological description, illustrations, and comparative interpretation of the new taxon. An updated phylogenetic backbone tree of Pleurotheciaceae is also presented, improving resolution of intergeneric relationships within the family. The discovery of <i>N. aquaticus</i> not only expands the taxonomic framework of Pleurotheciaceae but also contributes to a deeper understanding of the species richness, ecological roles, and biogeographic distribution of lignicolous freshwater fungi in Southwest China, particularly in the underexplored region of Guizhou Province.