Abstract Taxonomy within Hymenophyllum subgenus Mecodium (Hymenophyllaceae) has long presented significant challenges due to high morphological similarity among species. In this study, we conduct a taxonomic revision by combining a literature review, morphological examination of herbarium specimens, field investigations, and phylogenetic analyses based on several chloroplast markers (rbcL, accD, rps4, rbcL-accD, and rps4-trnS). Our revision yields an updated checklist of Chinese Mecodium, comprising 11 species and one variety. Integrating four Hymenophyllum-associated fossils, we performed divergence time estimation using both CladeDate and tip-dating methods. We infer for the subgenus Mecodium an origin in the Palaeogene, and a single arrival in Continental Asia dated from the Eocene. Major diversification events in Asia appear to coincide with the Himalayan orogeny and Miocene climatic shifts. Biogeographical reconstruction indicates multiple dispersal routes, including transoceanic movement from East Asia to North America and southeastward expansion from the Himalayan region within Asia. These findings offer new insights into the evolutionary history of this taxonomically complex fern group.
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