| Summary: | Microfungi associated with woody plants on the Qinghai–Tibet Plateau (QTP) were investigated, and four collections associated with <i>Potentilla fruticosa</i> were obtained from Gansu and Qinghai provinces in China. Morphologically, they line well with <i>Lentitheciaceae</i> in having subglobose to globose ascomata with brown setae on the papilla but can be distinguished from other genera by its superficial, globose, black, thick-walled ascomata, and fusiform, hyaline (rarely pale brown), one-septate ascospores, surrounded by an entire mucilaginous sheath. The phylogenetic analyses based on a combined SSU, ITS, LSU and <i>TEF</i>1-α sequence data showed that four isolates formed a monophyletic clade among the genera of <i>Lentitheciaceae</i>, and present as a distinct lineage (sister clade to <i>Darksidea</i>). Therefore, we introduce a new genus <i>Crassoascoma</i>, with <i>C. potentillae</i> as the type to accommodate these taxa. Detailed description and illustration are provided, and the establishment of new taxa is justified with morphology and phylogenetic evidence.
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