Testing and using complete plastomes for authentication of medicinal Polygonatum species (Asparagaceae)

Polygonati Rhizoma, a traditional Chinese medicine important to the pharmaceutical and food industries, is frequently adulterated with morphologically similar congeneric species, posing quality and effectiveness issues for the products. Accordingly, the accurate and sensitive authentication of medicinal Polygonatum species is vital to the standardization of Polygonati Rhizoma products. In view of the difficulties in morphological analysis and the use of standard DNA barcodes for authentication of medicinal Polygonatum species, an alternative authentication method is needed. Based on inter- and intraspecies sampling, phylogenetic and genetic distance analyses were performed to evaluate the discriminative power of complete plastomes for the identification of Polygonatum species. The results indicate that the genetic criteria of complete plastomes are in good correspondence with species boundaries and therefore can be used for unambiguous identification of medicinal Polygonatum species and morphologically similar congeners, which verifies the theoretical prediction that the application of genome skimming to generate complete plastomes as molecular tags can serve as an effective and accurate method to detect whether Polygonati Rhizoma is adulterated with congeneric species. Additionally, in this study, a taxonomically well-curated and high-resolution reference plastome superbarcode library for Polygonatum was developed for the first time, providing a valuable genetic resource for the application of genome skimming to monitor and control the production and trade of Polygonati Rhizoma to guarantee the effectiveness of downstream products. The findings also provide new insights to clarify the taxonomic ambiguities of the generic circumscription of Polygonatum and Heteropolygonatum, as well as the species delimitation of Polygonatum cyrtonema, Polygonatum nodosum, and Polygonatum punctatum, which will contribute to proper exploitation and conservation of Polygonatum species.