Complete Chloroplast Genome Sequence of Endangered Species in the Genus Opisthopappus C. Shih: Characterization, Species Identification, and Phylogenetic Relationships.

Opisthopappus C. Shih is a rare genus of the Asteraceae family native to the Taihang Mountains in China. Due to the narrow distribution area, poor reproduction ability and human harvesting, Opisthopappus is threatened by extinction. However, the limited genetic information within Opisthopappus impede understanding of the conservation efforts and bioprospecting. Therefore, in this study, we reported the complete chloroplast (cp) genome sequences of two Opisthopappus species, including Opisthopappus taihangensis and Opisthopappus longilobus . The cp genomes of O. taihangensis and O. longilobus were 151,117 and 151,123 bp, which contained 88 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. The repeat sequences, codon usage, RNA-editing sites, and comparative analyses revealed a high degree of conservation between the two species. The ycf 1 gene was identified as a potential molecular marker. The phylogenetic tree demonstrated that O. longilobus was a separate species and not a synonym or variety of O. taihangensis. The molecular clock showed that two species diverge over a large time span, O. longilobus diverged at 15.24 Mya (Million years ago), whereas O. taihangensis diverged at 5.40 Mya We found that Opisthopappus and Ajania are closely related, which provides new ideas for the development of Opisthopappus. These results provide biological information and an essential basis to understand the evolutionary history of the Opisthopappus species, which will aid in the future the bioprospecting and conservation of endangered species.