Applications and challenges of DNA barcoding in rapid radiation groups: Rhodiola (Crassulaceae) as a case study

Rhodiolae Crenulatae Radix et Rhizoma (Hongjingtian in Chinese, RCRR), the roots and rhizomes of Rhodiola crenulata and its application in the medicinal market is very chaotic. In this study, DNA barcoding database and identification engine of Rhodiola species were established, decoction pieces from the medicinal market were identified, and the application and challenges of DNA barcoding in the rapid radiation of Rhodiola species were analyzed. This study provides reference for the protection, rational development, and utilization of endangered resources within Rhodiola species. A total of 50 original plant samples from 20 species of the genus Rhodiola from Hebei, Xinjiang, Tibet, Jilin, and other major production areas were collected. Theses samples cover the typical distribution area (Qinghai-Tibetan Platea) of Rhodiola species and other scattered alpine regions (Changbai Mountain, Taibai Mountain, Lushan Mountain, etc.), it encompasses all Rhodiola species with thick rhizomes in China. ITS2 and psbA-trnH barcode of Rhodiola database (BORD) were established and an identification engine named Rhodiola-IDE was developed. The stability and accuracy of the standard DNA barcoding database were evaluated using two datasets. Rhodiola-IDE identified 31 decoction pieces of RCRR from the medicinal material market. The BORD containing 1 532 sequences of 88 Rhodiola species has been established, and the identification efficiency results showed good accuracy and stability. According to the Chinese Pharmacopoeia (2020 edition), 23 samples (74.2%) were identified as authentic R. crenulata, while the rest of the marketed varieties were R. kirilowii, R. dumulosa, and R. fastigiata. The product label “Larger flower, Hongjingtian” was identified as R. crenulata. Samples labeled as “Smaller flower, Hongjingtian” were identified as R. crenulata, R. kirilowii, and R. fastigiata. ITS2 and psbA-trnH barcodes can identify monophyletic groups represented by R. crenulata. However, for non-monophyletic species, it is necessary to collect as many samples as possible and combine them with multiple markers for joint identification. This study discussed the application and challenges of DNA barcodes in Rhodiola under rapid radiation conditions, providing a scientific basis for the rational development and utilization of Rhodiola varieties.