Plastid Phylogenomics Provide Evidence to Accept Two New Members of <i>Ligusticopsis</i> (Apiaceae, Angiosperms)

<i>Peucedanum nanum</i> and <i>P. violaceum</i> are recognized as members of the genus <i>Peucedanum</i> because of their dorsally compressed mericarps with slightly prominent dorsal ribs and narrowly winged lateral ribs. However, these species are not similar to other <i>Peucedanum</i> taxa but resemble <i>Ligusticopsis</i> in overall morphology. To check the taxonomic positions of <i>P. nanum</i> and <i>P. violaceum</i>, we sequenced their complete plastid genome (plastome) sequences and, together with eleven previously published <i>Ligusticopsis</i> plastomes, performed comprehensively comparative analyses. The thirteen plastomes were highly conserved and similar in structure, size, GC content, gene content and order, IR borders, and the patterns of codon bias, RNA editing, and simple sequence repeats (SSRs). Nevertheless, twelve mutation hotspots (<i>mat</i>K, <i>ndh</i>C, <i>rps</i>15, <i>rps</i>8, <i>ycf</i>2, <i>ccs</i>A-<i>ndh</i>D, <i>pet</i>N-<i>psb</i>M, <i>psb</i>A-<i>trn</i>K, <i>rps</i>2-<i>rpo</i>C2, <i>rps</i>4-<i>trn</i>T, <i>trn</i>H-<i>psb</i>A, and <i>ycf</i>2-<i>trn</i>L) were selected. Moreover, both the phylogenetic analyses based on plastomes and on nuclear ribosomal DNA internal transcribed spacer (ITS) sequences robustly supported that <i>P. nanum</i> and <i>P. violaceum</i> nested in <i>Ligusticopsis</i>, and this was further confirmed by the morphological evidence. Hence, transferring <i>P. nanum</i> and <i>P. violaceum</i> into <i>Ligusticopsis</i> genus is reasonable and convincing, and two new combinations are presented.