Phylogeographic and phylogenetic analysis for Tripterygium species delimitation

Tripterygium wilfordii (Celastraceae) is a traditional Chinese medicine; and the dried root and rhizome constitute the main officinal parts. Tripterygium wilfordii has been identified as a potential candidate for the treatment of systemic lupus erythematosus, rheumatoid arthritis, nephritis, asthma, leprosy, and cancer. The phylogenetic relationships within the Tripterygium genus are ambiguous; thus, our aim is to clarify the relationships within this genus using phylogeographic and phylogenetic analyses. Here, we first sequenced three plastid DNA regions (i.e., psbA-trnH, rpl32-trnL, and trnL-trnF) and found that Tripterygium hypoglaucum and T. wilfordii were clustered together based on the strength of the topology in the phylogenetic analysis: T. hypoglaucum is polyphyletic, and T. wilfordii is paraphyletic. A spatial analysis of molecular variance showed that the best group value is 4, and the groups were almost consistent with the topology of in the phylogenetic analysis. The Mantel analyses of Tripterygium using IBD web showed statistically significant relationships between genetic and geographical distance distributions (r = .3479, p < .0001). The molecular dating using Fossil calibration indicated that the divergence in Tripterygium was approximately 8.13 Ma. Furthermore, we also analyzed four DNA regions (i.e., ITS2, psbA-trnH, matK, and rbcL) that were obtained from the NCBI nucleotide database; these results showed that T. wilfordii and T. hypoglaucum clustered together, while Tripterygium regelii represented a separate cluster. Tripterygium hypoglaucum and T. wilfordii were never distinct lineages, and the species circumscriptions are artificial. We propose that T. wilfordii and T. hypoglaucum are conspecific, while T. regelii likely constitutes a separate species.