Distribution and taxonomic identity of <i>Cyclosorus parasiticus</i> (Thelypteridaceae) in Korea

Thelypteridaceae is a taxonomically ambiguous family with generic boundaries defined by extensive morphological variation and frequent interspecific convergence. Consequently, <i>Cyclosorus parasiticus</i> (L.) Farw. has been classified under several genera by many researchers. Although its occurrence in Korea is documented in the literature, its morphological identity remains unverified due to a lack of extant specimens. In this study, we confirmed the existence of <i>C. parasiticus</i> in Korea through discoveries in stone wall crevices in Dongheung-dong, Seogwipo-si and on Jigwido Island near Jejudo Island. Morphologically, <i>C. parasiticus</i> is most similar to <i>C. dentatus</i> (Forssk.) Ching; however, it is clearly distinguished by the lack of reduced (or only slightly) proximal pinnae in fertile fronds, the presence of reddish-orange glands on the veinlets, and significantly longer hairs (ca. 1 mm) on the fronds. In addition, the relationships among taxa of the genus <i>Cyclosorus</i> were confirmed through a molecular phylogenetic analysis using chloroplast <i>rbcL</i> gene sequences. <i>C. parasiticus</i> formed a group with <i>C. acuminatus</i> (Houtt.) Nakai and <i>C. dentatus</i> but formed sister lineages with <i>C. interruptus</i> (Willd.) H. Itô and <i>C. penangianus</i> (Hook.) Copel. The analysis of the relationships between the related taxa suggested that the genus boundaries of the group to which <i>C. parasiticus</i> belongs have not been clearly resolved. Based on these results, we concluded that maintaining the name <i>C. parasiticus</i> is at present taxonomically appropriate. Additionally, this study provides photographs and a key to distinguish it from closely related taxa.