Molecular evidence provides new insights into the evolutionary origin of an ancient traditional Chinese medicine, the domesticated "Baizhi".

Introduction: "Baizhi" is a famous herbal medicine in China, and it includes four landraces named as 'Hangbaizhi', 'Chuanbaizhi', 'Qibaizhi', and 'Yubaizhi'. Long-term artificial selection had caused serious degradation of these germplasms. Determining the wild progenitor of the landraces would be benefit for their breed improvements. Previous studies have suggested var. , var. , or as potential candidates, but the conclusion remains uncertain, and their phylogenetic relationships are still in controversy.

Methods: In this study, the genetic variation and phylogenetic analyses of these species and four landraces were conducted on the basis of both the nrITS and plastome datasets.

Results: Genetic variation analysis showed that all 8 population of four landraces shared only one ITS haplotype, meanwhile extremely low variation occurred within 6 population at plastid genome level. Both datasets supported the four landraces might be originated from a single wild germplasm. Phylogenetic analyses with both datasets revealed largely consistent topology using Bayesian inference and Maximum likelihood methods. Samples of the four landraces and all wild var. formed a highly supported monophyletic clade, and then sister to the monophyly clade comprised by samples of , while four landraces were clustered into one clade, which further clustered with a mixed branches of and var. to form sister branches for plastid genomes. Furthermore, the monophyletic var. was far distant from the var. -"Baizhi" clade in phylogeny. Such inferences was also supported by the evolutionary patterns of nrITS haplotype network and K2P genetic distances. The outcomes indicated var. is most likely the original plant of "Baizhi".

Discussion: Considering of phylogenetic inference and evolutionary history, the species-level status of var. should be accepted, and the taxonomic level and phylgenetic position of should be further confirmed. This study preliminarily determined the wild progenitor of "Baizhi" and clarified the phylogenetic relationships among var. , var. and , which will provide scientific guidance for wild resources protections and improvement of "Baizhi".