Comparative analysis of chloroplast genomes of Sanguisorba species and insights into phylogenetic implications and molecular dating

<pre class="js_message_plain ng-binding"><em>Sanguisorba</em> is a small genus, which consists of about 15 species widely distributed in North America and Eurasia. Previous studies on <em>Sanguisorba</em> are useful for understanding of phylogeny and chloroplast (cp) genome evolution of <em>Sanguisorba</em>. However, the cp genome resources of <em>Sanguisorba</em> are still limited, and the phylogeny and molecular dating for <em>Sanguisorba</em> and its relatives still need further explored. Here, we reported four cp genomes of <em>Sanguisorba</em> and conducted comparative analysis of the four <em>Sanguisorba</em> cp genomes plus five previously published ones. The nine cp genomes of <em>Sanguisorba</em> have typical tetrad quadripartite structure, with a total length of 154 282 to 155 730 bp, and their gene content, gene structure, and gene order are relatively conservative. The analysis of single copy (SC)/inverted repeat (IR) boundaries shows very slight boundary differences in <em>Sanguisorba</em> cp genomes. Eight variation hotspots were screened as excellent candidate markers of <em>Sanguisorba</em>. Phylogenetic analysis indicated <em>Sanguisorba</em> was monophyletic and was a member of tribe Agrimonieae subtribe Sanguisorbinae. Within <em>Sanguisorba</em>, <em>S. filiformis</em> is a sister group of six other taxa in the present sampling. Estimation of the divergence times indicated that subtribes Agrimoniinae and Sanguisorbinae diverged at the transition between the Oligocene and the Miocene, and divergent times of Agrimonieae genera ranged from the late Miocene to the Middle Pleistocene. This study enriches the available cp genome resources of <em>Sanguisorba</em>, and it is of great significance to further study the phylogeny and evolution of <em>Sanguisorba</em> and its relatives.</pre>