High species discrimination in Pedicularis (Orobanchaceae): Plastid genomes and traditional barcodes equally effective via parsimony-informative sites.

Complete plastid genomes have been proposed as potential "super-barcodes" for plant identification and delineation, particularly in cases where standard DNA barcodes may be insufficient. However, few studies have systematically addressed how taxonomic complexity, especially in rapidly radiating lineages with intricate evolutionary histories, might influence the efficacy of plastome-scale barcodes. Pedicularis is a hyperdiverse genus in the Himalaya-Hengduan Mountains, and previous studies have demonstrated high discriminatory power of the standard barcodes within this genus. Therefore, Pedicularis serves as a model for investigating the key plastome-sequence characteristics and biological phenomena that determine species-discrimination capacity. In this study, we evaluated 292 plastomes representing 96 Pedicularis species to compare the discriminatory power of complete plastid genomes with of standard DNA barcodes. Our results revealed that the traditional standard barcode combination (nrITS + matK + rbcL + trnH-psbA) achieved the highest discrimination rates (81.25%), closely followed by the plastid large single copy (LSC) region (80.21%), then by full plastome, the supermatrix of protein-coding genes, and hypervariable regions (79.17%). Notably, the matK and ycf1 gene alone could discriminate 78.13% of species. Key determinants of species discrimination by integrating alignment length (AL) and the proportion of parsimony-informative sites (PPIS), as well as conserved genes under relaxed selection exhibiting stronger discriminatory capacity. Unlike previous studies that demonstrated superior discrimination rates of plastome-scale barcodes, this study reveals a notable exception of minimal differences between traditional DNA and plastome-scale barcodes that appearing linked to Pedicularis' specific biological habits and potentially reflecting unique evolutionary patterns in the plastid genome.