Taxonomic identity of Crepidiastrum ×nakaii recorded on Hongdo Island

The plant known as “Hong-do-go-deul-ppae-gi” on Hongdo Island, belonging to the genus Crepidiastrum, has been recorded as C. ×nakaii, a hybrid between C. denticulatum and C. platyphyllum. During a survey of the flora of Hongdo Island, we reexamined the taxonomic identity of “Hong-do-go-deul-ppae-gi”. The morphological traits, geographical distribution, and internal transcribed spacer (ITS) sequences of “Hong-do-go-deul-ppae-gi” were compared to related species within the genus. A morphological examination revealed that the plant was similar to C. lanceolatum in that it has subshrub stems with caudex stout, 8 inner involucrals bracts, and 10 to 12 florets. In contrast, similarities to C. denticulatum were observed in terms of radical leaves deciduous in the flowering period, cauline leaves membranous with acute serrations, and beaked achenes. Furthermore, C. denticulatum and C. lanceolatum grew on Hongdo Island and nearby areas, but C. platyphyllum was not distributed in these areas. The results of morphological and distributional investigations revealed that the Hongdo Island plant should be regarded as C. ×muratagenii, a hybrid between C. denticulatum and C. lanceolatum, not C. ×nakaii, which is a hybrid between C. denticulatum and C. platyphyllum. However, the resolution of the ITS sequences was insufficient such that we could not separate the examined species.