Molecular phylogeny of the platycodonoid group (Campanulaceae s.Str.) with special reference to the circumscription of Codonopsis

Abstract

Phylogenetic analyses of 41 taxa representing all genera except Ostrowskia of the platycodonoid group were done using sequences of five DNA fragments from the chloroplast and nuclear genomes. The results show that the platycodonoid group is a monophyletic group, and that four major clades can be recognized: (1) the Platycodon clade with colporate pollen, including Platycodon, Canarina, Cyclocodon, and Echinocodon; (2) the Cyananthus clade with colpate pollen and a superior ovary, including only Cyananthus; (3) the long-colpus clade with long-colpus pollen, an inferior ovary, and a disc or glands, including Codonopsis subg. Codonopsis, Campanumoea, and Leptocodon; and (4) the short-colpus clade with short-colpus pollen, an inferior ovary, and without a disc or glands, including Codonopsis subg. Pseudocodonopsis, subg. Obconicicapsula, and C. purpurea of Codonopsis subg. Codonopsis. These four major clades are strongly supported and well correlated with pollen type and morphology. The results support the separation of Cyclocodon from Codonopsis as a genus. The results also indicate that Campanumoea and Leptocodon should be merged with Codonopsis, whereas all taxa of the short-colpus clade should be separated from Codonopsis.