Freshwater fungi in South China, with two new species and one new record in Bambusicolaceae and Occultibambusaceae (Pleosporales, Dothideomycetes)

Bambusicolaceae and Occultibambusaceae are two closely related families in Pleosporales (Dothideomycetes) that are predominantly associated with bamboo and woody substrates in terrestrial habitats, but their diversity and ecological roles in freshwater environments remain poorly understood. In this study, three freshwater fungal isolates were collected from submerged wood/bamboo in Guangdong and Yunnan Provinces, China. Morphological examinations combined with multigene phylogenetic analyses (ITS, LSU, RPB 2, SSU and TEF 1α) were conducted to clarify their taxonomic placement. Two new species, Bambusicola submersa and Brunneofusispora submersa , are introduced based on distinct morphological characters and strong phylogenetic support. In addition, Seriascoma honghense is reported from freshwater for the first time, representing the first freshwater record for the genus Seriascoma . Phylogenetic and morphological evidence further supports the synonymization of Corylicola hydei with C. italica . Comparative analyses of host association and habitat preference reveal contrasting evolutionary patterns between the two families. Bambusicolaceae exhibits relatively flexible host utilization and limited freshwater diversification, whereas Occultibambusaceae shows stronger host conservatism toward bamboo coupled with repeated transitions into freshwater habitats. These results highlight the importance of freshwater ecosystems in shaping fungal diversification and emphasize the need for expanded sampling across aquatic and bamboo-associated substrates to better understand the evolutionary history of these pleosporalean fungi.