Morphological and molecular evidence of the hybrid origin of Crepidiastrum ×muratagenii in Korea

The plant “Hong-do-go-deul-ppae-gi” has been considered as Crepidiastrum × muratagenii, a hybrid between C. denticulatum and C. lanceolatum, based on its morphological traits and geographical distribution. To reveal the hybrid origin of Hong-do-go-deul-ppae-gi, we examined additional morphological traits of this plant and its putative parents (C. denticulatum, C. lanceolatum, C. platyphyllum) and analyzed one nuclear ribosomal internal transcribed spacer (ITS) region and four chloroplast regions (trnT-L, trnL-F, rpl16 intron, and rps16 intron). As a result of examining the morphological traits, putative hybrid individuals were classified into three types based on the habit, cauline leaf, outer phyllary, and achene beak traits. A molecular analysis found that the ITS sequences of Type 1 and Type 2 individuals showed additive species-specific sites of C. denticulatum and C. lanceolatum. Plastid sequences of Type 1 and Type 2 individuals showed C. denticulatum and C. lanceolatum sequences, respectively. However, Type 3 individuals had ITS and plastid sequences corresponding to C. denticulatum. Accordingly, Type 1 and Type 2 individuals not only share morphological traits with C. denticulatum and C. lanceolatum but also show additive species-specific sites for C. denticulatum and C. lanceolatum, and not C. platyphyllum, supporting its origin as a hybrid between C. denticulatum and C. lanceolatum. Type 3 had morphological traits similar to other hybrid types but was distinguished with respect to outer phyllaries and demonstrated some resemblance to C. denticulatum. In a molecular analysis, Type 3 was found to be identical with regard to the sequence of C. denticulatum and was judged to be an ecological variation of C. denticulatum.