A new species, Antrophyum nambanense , is described here based on the evidence from morphology and molecular phylogeny. Morphologically, short taeniform soral paraphyses and large fronds are the diagnostic characteristics of A. nambanense . Phylogenetically, it is most closely related to A. annamense , but can be readily distinguished from A. annamense by taeniform soral paraphyses (vs. filiform). We suggest A. nambanense is an allopolyploid of hybrid origin involving A. annamense and A. henryi , based on the evidence of morphology, phylogenetic position, chromosome number, and partially malformed spores . A description, photographs of key characters, distribution, conservation status, and ecology of the new species are presented. In addition, A. nambanense is also the first confirmed species with chlorophyllous spores in Antrophyum . Lastly, an updated key to all known Antrophyum species in Vietnam, including A. henryi as a new record for the country, is provided.