| Summary: | Hymenasplenium obtusidentatum, a new fern species of the H. excisum subclade of Hymenasplenium (Aspleniaceae) from south and southwestern China was described. Molecular phylogenetic analyses and morphological observations of H. obtusidentatum and related species clearly indicated that this is a distinct taxonomic entity. Phylogenetically, H. obtusidentatum was confirmed to represent a diverging lineage in the H. excisum subclade of Hymenasplenium and was closely related to one lineage that includes accessions identified as H. obscurum, H. pseudobscurum and H. tholiformis. Morphologically, H. obtusidentatum can be distinguished by the combination of its lamina base truncate, stipe not shiny and with color of reddish brown to dark brown, and pinna marginal teeth that are not sharp, but blunt or rounded. A complete species description and comparison with related species in the H. excisum subclade were provided. The holotype of H. obtusidentatum was designated.
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