Species delimitation in the phegopteris decursivepinnata polyploid species complex (Thelypteridaceae)

Phegopteris decursivepinnata harbors diploid and tetraploid strains, forming a polyploid species complex together with P. koreana. Hybridization and polyploidization in the complex blur species boundar-ies, making it challenging to apply the proper taxonomic treatment. Ploidy determinations, phylogenetic analyses, and morphological investigations to elucidate the origins of the polyploid species and improve species classification for the P. decursivepinnata species complex are reported. Ploidy determinations and phylogenetic analyses revealed that diploid members of the complex were separated into two groups, a diploid P. decursivepinnata and a group consisting of Thelypteris itoana and a diploid P. koreana. The tetraploid P. decursivepinnata was shown to be an allotetraploid derived from hybridization between the two diploid groups. The samples of P. koreana revealed to be diploid suggested intraspecific cytotypic variation in P. koreana. The diploid P. koreana was genetically and morphologically indistinguishable from the diploid T. itoana. The diploid members of the complex previously treated as P. decursivepin-nata are described as a new species, P. taiwaniana; and T. itoana is placed in synonymy under P. koreana.