Phylogenetic Insights Reveal New Taxa in Thyridariaceae and Massarinaceae

Pleosporales is a highly diverse (and the largest) order in Dothideomycetes, and it is widespread in decaying plants in various environments around the world. During a survey of fungal diversity in Sichuan Province, China, specimens of hyphomycetous and <i>Thyridaria</i>-like fungi were collected from dead branches of pine trees and cherry trees. These taxa were initially identified as members of Massarinaceae and Thyridariaceae through morphological examination. Phylogenetic analyses of the Thyridariaceae, combining ITS, SSU, LSU, <i>RPB2</i>, and <i>TEF1</i> sequence data, indicated a distinct clade sister to <i>Pseudothyridariella</i> and <i>Thyridariella</i>, distinct from any genus in the family. Thus, a new genus, <i>Vaginospora</i>, is proposed to accommodate the type species <i>Vaginospora sichuanensis</i>, which is characterized by semi-immersed globose to oblong ascomata with an ostiolar neck, cylindrical to clavate asci with an ocular chamber, and hyaline to dark brown, fusiform, 3–5-transversely septate ascospores with an inconspicuous mucilaginous sheath. Based on the morphological comparisons and multi-locus phylogenetic analyses (ITS, SSU, LSU, <i>RPB2</i>, and <i>TEF1</i>) of the Massarinaceae, we have identified three collections belonging to the genus <i>Helminthosporium</i>, leading us to propose <i>H. filamentosa</i> sp. nov., <i>H. pini</i> sp. nov., and <i>H. velutinum</i> as a new host record. According to Phylogenetic analysis, <i>H. pini</i> formed an independent clade sister to <i>H. austriacum</i> and <i>H. yunnanense</i>, and <i>H. filamentosa</i> represents the closest sister clade to <i>H. quercinum</i>. <i>Helminthosporium pini</i> is distinct from <i>H. austriacum</i> by the shorter conidiophores and <i>H. yunnanense</i> by the longer and wider conidia. The <i>H. filamentosa</i> differs from <i>H. quercinum</i> in having longer conidiophores and smaller conidia. This study extends our understanding of diversity within Thyridariaceae and <i>Helminthosporium</i>. Our findings underscore the rich biodiversity and potential for discovering novel fungal taxa within these groups.