Freshwater fungi consist of a highly diverse group of organisms in freshwater habitats worldwide. During a survey of fungal diversity in freshwater habitats across different regions of Jiangxi Province, China, four freshwater fungi were collected. To study their phylogenetic relationships, the internal transcribed spacer (ITS1-5.8S-ITS2), large subunit (28S, LSU), small subunit (18S, SSU), and RNA polymerase II subunit (RPB2) genes were selected for phylogenetic analyses. Based on morphology coupled with phylogenetic analysis, these strains were confirmed to belong to Phaeoisaria, Pleurothecium, and Pseudodactylaria. Among them, three fungi were confirmed as the new species, namely, Pleurothecium lignicola (Pleurotheciaceae), Pseudodactylaria jiangxiensis (Pseudodactylariaceae), and Ps. lignicola (Pseudodactylariaceae). One species was identified as Phaeoisaria filiformis (Pleurotheciaceae), a new record of this species in China. All species were compared with other similar species, and detailed descriptions, illustrations, and phylogenetic data were provided.

In terms of morphology, ecology, and phylogeny, Lentitheciaceae species exhibit an enormous diversity. They have a cosmopolitan distribution worldwide, and lead diverse lifestyles. A novel species in Lentitheciaceae, Pseudosetoseptoria jiangxiensis occurring on decaying culms of bamboo in Jiangxi province, China is described and illustrated. Morphologically, Pseudosetoseptoria jiangxiensis has dark brown to black, semi-immersed, carbonaceous, pycnidial conidiomata and hyaline, obovoid, elliptic, or nearly spherical, aseptate conidia with minute guttules. Maximum likelihood and Bayesian inference analyses of combined ITS, LSU, SSU and tef1-α sequence data were used to clarify the phylogenetic affinities of the species.