Plastomes of (Orchidaceae) and Phylogenetic Implications.

The genus is a small genus of only five species distributed across Asia, including , , , and which is of great medicinal importance. Furthermore, this genus is a member of the key tribe Arethuseae (Orchidaceae), harboring an extremely complicated taxonomic history. Recently, the monophyletic status of has been challenged, and the phylogenetic relationships within this genus are still unclear. The plastome, which is rich in both sequence and structural variation, has emerged as a powerful tool for understanding plant evolution. Along with four new plastomes, this work is committed to exploring plastomic markers to elucidate the phylogeny of . Our results reveal considerable plastomic differences between and the other three taxa in many aspects. Most importantly, the specific features of the IR junction patterns, novel pttRNA structures and codon aversion motifs can serve as useful molecular markers for phylogeny. Moreover, based on maximum likelihood and Bayesian inference methods, our phylogenetic analyses based on two datasets of Arethuseae strongly imply that is non-monophyletic. Accordingly, our findings from this study provide novel potential markers for species identification, and shed light on the evolution of and Arethuseae.