Plastid genome insight to the taxonomic problem for Aconitum pendulum and A. flavum (Ranunculaceae)

As the original species of traditional Chinese medicine “Tie Bang Chui,” the distribution of the Aconitum pendulum and A. flavum almost wholly overlap. This study compared the complete plastid genome (plastome) of A. flavum and A. pendulum to assess their phylogenetic relationships. The plastome sizes of A. flavum range from 155,642 bp ( A. flavum MW839582) to 155,717 bp ( A. flavum MW839579), A. pendulum range from 155,667 bp ( A. pendulum MW839577) to 155,713 bp ( A. pendulum MW839581). The plastomes are identical, with 131 genes, including eight rRNA genes, 37 tRNA genes, 86 protein-coding genes, and one pseudogene. Long repeats sequences were present in both coding regions and non-coding regions. There were highly variables in the non-coding region both in intra- and interspecies levels. Nine highly variable regions were detected that were suitable for phylogenetic analysis. Moreover, in the protein-coding region, rpo C1 was more divergent in intraspecies level. Furthermore, protein-coding genes were ideal for species delimitation in Aconitum species than highly variated regions. Phylogenetic analysis suggests that individuals of A. pendulum and A. flavum were not clustered by species. It might be affected by geographical and ecological factors. A. flavum and A. pendulum have similar morphological characteristics, overlap geographical distribution, highly identical plastome structure, and indistinct phylogenetic relationship. Further research for the two species is necessary, such as population genetic study, to reveal they are the same or two distinct species.