Systematics of the <i>Cosmospora viliuscula</i> species complex

The genus Cosmospora includes nectrioid fungi that grow on polypores and xylariaceous fungi. The collections growing on xylariaceous fungi have been identified recently as Cosmospora viliuscula. In this paper the phylogeny and taxonomy of C. viliuscula are investigated. A phylogeny was generated with maximum likelihood and Bayesian inference methods applied to a three-partition dataset (ITS, 28S, MCM7-RPB1-TUB2). Based on these results, we demonstrate that Cosmospora viliuscula represents a diverse species complex comprising more than 10 species. Seven new species are described, including three single-strain lineages, and the sexual states of C. arxii and C. khandalensis are described for the first time. The sexual states of these fungi tend to have a high degree of morphological homoplasy, making it difficult to differentiate among them based on morphological characters alone. However, the apparent host specificity of species in this complex aide in the diagnosis of these fungi. In addition, the RPB1 marker provides sufficient resolution to distinguish these fungi.