Insights into phylogenetic relationships of Veronica species (Plantaginaceae) based on comparative chloroplast genomics.

Veronica L. is one of the most species-rich genera in Plantaginaceae and several species have medicinal, horticultural, or ecological value. In this study, the complete chloroplast genomes of three Veronica species were assembled and annotated using Illumina sequencing data. The plastomes exhibited a typical quadripartite structures, with total lengths of 150,202 bp for Veronica biloba L., 151,159 bp for Veronica ciliata Fisch. and 151,098 bp for Veronica vandellioides Maxim. Each genome contained 130-132 unique genes, including 86-87 protein-coding genes, 36-37 tRNA genes, and 8 rRNA genes. Comparative analyses of 24 Veronica plastomes indicated that the IR/SC junctions were largely conserved, although slight boundary shifts occurred around rps19, ndhF, and ycf1. Forward, palindromic, complement, and reverse repeats were detected, and A/T mononucleotide repeats were the dominant SSR type. Nucleotide diversity analysis identified rpl32-trnL, trnK-rps16, rpl32, ycf1, ndhF, accD, matK, and rpoB as highly variable regions. Phylogenetic analyses recovered Veronica as a well-supported monophyletic lineage and clarified the plastid positions of the three newly sequenced species. Divergence time estimation suggested that the estimation suggested of Veronica was around 14.9 Ma, with V. biloba, V. ciliata and V. vandellioides diverging approximately 3.9 Ma, 0.6 Ma, and 6.9 Ma, respectively. Because the analyses were based on plastid genomes, the inferred topology should be interpreted as chloroplast phylogenetic evidence rather than a complete species-history reconstruction. These results provide plastome resources and molecular evidence for taxonomy, species identification, and future evolutionary studies of Veronica.