<br> Lignicolous freshwater fungi play an important role in nutrient cycling and the maintenance of biodiversity within freshwater ecosystems. Recent intensive studies, particularly in Asia, have greatly advanced understanding of their taxonomy, diversity, and ecology. Yunnan and Guizhou provinces in southwestern China represent one of the most active regions for freshwater fungal research due to their complex topography, diverse freshwater bodies, and rich biodiversity. As part of a comprehensive investigation of lignicolous freshwater fungi in southwestern China, specimens were collected from rivers and plateau lakes. Multi-gene phylogenetic analyses based on a combined LSU, ITS, SSU,<br> rpb<br> 2, and<br> tef<br> 1-α dataset revealed that four monotypic genera,<br> Aquimonospora<br> ,<br> Multiseptisporium<br> ,<br> Paradiplococcium<br> , and<br> Platytrachelon<br> , form a distinct clade within Diaporthomycetidae families<br> incertae sedis<br> and are closely related to Melanascomaceae, Neodictyosporiaceae, Papulosaceae, and Pseudostanjehughesiaceae. Accordingly, a new family, Platytrachelaceae, is proposed to accommodate these genera. In addition, the genus<br> Multiseptisporium<br> is established to accommodate the type species<br> M. aquaticum<br> sp. nov<br> ., which produces sporidesmium-like conidia. This study highlights the phylogenetic diversity and morphological complexity of sporidesmium-like taxa and underscores the importance of integrating morphological and phylogenetic evidence to resolve their taxonomic relationships. The findings enrich the known diversity of lignicolous freshwater fungi in Yunnan and Guizhou and provide new insights into their taxonomy and ecological adaptation within freshwater ecosystems.<br>
