The fungal genus Curvularia includes numerous plant pathogens and some emerging opportunistic pathogens of humans. In a previous study we used morphology and sequences of the nuclear ribosomal internal transcribed spacer region (ITS) and the glyceraldehyde-3-phosphate dehydrogenase (gpd) gene to identify species within a set of 99 clinical Curvularia isolates from the USA. Seventy-two isolates could be identified while the remaining 27 isolates belonged in three unclassified clades that were tentatively labelled Curvularia sp. I, II and III. In the present study, we further assess the taxonomic placement of these isolates using sequences of ITS, gpd, the large subunit rDNA, and the second largest subunit of RNA polymerase II. DNA sequence comparisons with a set of 87 isolates representing 33 Curvularia spp. and members of the closely-related genera Bipolaris and Exserohilum revealed that Curvularia sp. I, II and III represent novel lineages in Curvularia. These lineages are morphologically different from the currently accepted species. In the phylogenetic tree, Curvularia sp. I and sp. III were each split into two distinct lineages. Morphology and phylogeny supported the proposal of five new species, to be named C. americana, C. chlamydospora, C. hominis, C. muehlenbeckiae and C. pseudolunata. The concatenated 4-locus phylogeny revealed the existence of six clades in Curvularia, which are associated with particular morphological features. They were named after representative species, namely americana, eragrostidis, hominis, lunata, spicifera and trifolii.
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