Discriminating plants using the DNA barcode rbcLb: an appraisal based on a large data set

Abstract The ideal DNA barcode for plants remains to be discovered, and the candidate barcode rbc L has been met with considerable skepticism since its proposal. In fact, the variability within this gene has never been fully explored across all plant groups from algae to flowering plants, and its performance as a barcode has not been adequately tested. By analysing all of the rbc L sequences currently available in G en B ank, we attempted to determine how well a region of rbc L performs as a barcode in species discrimination. We found that the rbc L b region was more variable than the frequently used rbc L a region. Both universal and plant group‐specific primers were designed to amplify rbc L b, and the performance of rbc L a and rbc L b was tested in several ways. Using blast , both regions successfully identified all families and nearly all genera; however, the successful species identification rates varied significantly among plant groups, ranging from 24.58% to 85.50% for rbc L a and from 36.67% to 90.89% for rbc L b. Successful species discrimination ranged from 5.19% to 96.33% for rbc L a and from 22.09% to 98.43% for rbc L b in species‐rich families, and from 0 to 88.73% for rbc L a and from 2.04% to 100% for rbc L b in species‐rich genera. Both regions performed better for lower plants than for higher plants, although rbc L b performed significantly better than rbc L a overall, particularly for angiosperms. Considering the applicability across plants, easy and unambiguous alignment, high primer universality, high sequence quality and high species discrimination power for lower plants, we suggest rbc L b as a universal plant barcode.