Comparative Analysis of the Complete Plastid Genome of Five <i>Bupleurum</i> Species and New Insights into DNA Barcoding and Phylogenetic Relationship

<i>Bupleurum</i> L. (Apiaceae) is a perennial and herbal genus, most species of which have high medicinal value. However, few studies have been performed using plastome data in this genus, and the phylogenetic relationships have always been controversial. In this study, the plastid genomes of <i>Bupleurum chinense</i> and <i>Bupleurum commelynoideum</i> were sequenced, and their gene content, order, and structure were counted and analyzed. The only three published <i>Bupleurum</i> species (<i>B. boissieuanum</i>, <i>B. falcatum,</i> and <i>B. latissimum</i>) and other fifteen allied species were selected to conduct a series of comparative and phylogenetic analyses. The genomes of <i>B. chinense</i> and <i>B. commelynoideum</i> were 155,869 and 155,629 bp in length, respectively, both of which had a typical quadripartite structure. The genome length, structure, guanine and cytosine (GC) content, and gene distribution were highly similar to the other three <i>Bupleurum</i> species. The five <i>Bupleurum</i> species had nearly the same codon usages, and eight regions (<i>petN-psbM</i>, <i>rbcL-accD</i>, <i>ccsA-ndhD</i>, <i>trnK(UUU)-rps16</i>, <i>rpl32-trnL(UAG)-ccsA</i>, <i>petA-psbJ</i>, <i>ndhF-rpl32,</i> and <i>trnP(UGG)-psaJ-rpl33</i>) were found to possess relatively higher nucleotide diversity, which may be the promising DNA barcodes in <i>Bupleurum</i>. Phylogenetic analysis revealed that all <i>Bupleurum</i> species clustered into a monophyletic clade with high bootstrap support and diverged after the <i>Chamaesium</i> clade. Overall, our study provides new insights into DNA barcoding and phylogenetic relationship between <i>Bupleurum</i> and its related genera, and will facilitate the population genomics, conservation genetics, and phylogenetics of <i>Bupleurum</i> in Apiaceae.