Phylogeny of Panax using chloroplast trnC– trnD intergenic region and the utility of trnC– trnD in interspecific studies of plants

Sequences of the chloroplast trnC– trnD region and the internal transcribed spacer (ITS) regions of nuclear ribosomal DNA were obtained for all species of Panax L. (the ginseng plant genus, Araliaceae) to reconstruct phylogenetic relationships. The trnC– trnD phylogeny is congruent with the ITS phylogeny for the diploid taxa of Panax. This study is the first use of the trnC– trnD sequence data for phylogenetic analysis at the interspecific level. We evaluated this DNA region for its phylogenetic utility at the lower taxonomic level for flowering plants. The trnC– trnD region includes the trnC– petN intergenic spacer, the petN gene, the petN– psbM intergenic spacer, the psbM gene, and the psbM– trnD intergenic spacer. The petN and psbM genes are small, 90 and 104–114 bp across angiosperms, respectively, and have conserved sequences. We have designed universal amplification and sequencing primers within these two genes. Using these primers, we have successfully amplified the entire trnC– trnD region for a diversity of flowering plant groups, including Aralia L. (Araliaceae), Calycanthus L. (Calycanthaceae), Corylus L. (Betulaceae), Hamamelis L. (Hamamelidaceae), Hydrocotyle L. (Apiaceae), Illigera Blume (Hernandiaceae), Nelumbo Adans. (Nelumbonaceae), Nolana L. ex L.f. (Solanaceae), Prunus L. (Rosaceae), and Staphylea L. (Staphyleaceae). In Panax, the trnC– trnD region provides a similar number of informative phylogenetic characters as the ITS regions and a slightly higher number of informative characters than the chloroplast ndhF gene. We thus demonstrate the utility of the trnC– trnD region for lower-level phylogenetic studies in flowering plants.