New distribution records of two rare species of <i>Cynanchum</i> (Apocynaceae) in South Korea: <i>Cynanchum thesioides</i> (Freyn) K. Schum. and <i>Cynanchum chinense</i> R. Br.

Abstract

Cynanchum L. in the subfamily Asclepiadoideae (Apocynaceae) includes four recognized species on the Korean peninsula, two of which are native to South Korea. However, the species ranges in South Korea are poorly defined. During a field survey, we discovered C. thesioides, previously unrecorded in South Korea, in Gimpo-si, Gyeonggi-do, and found an additional population of C. chinense, for which only one population has been reported in South Korea. The two taxa are considered rare species with extremely restricted distributions in South Korea, especially C. thesioides. We provide fundamental information, including descriptions, images of the habitats and morphological characters, and a taxonomic key for identification and assessments of the conservation status of Cynanchum species in Korea.