Comparative Analysis of Chloroplast Genomes Across 20 Plant Species Reveals Evolutionary Patterns in Gene Content, Codon Usage, and Genome Structure

Chloroplast genomes are valuable tools for exploring plant evolution, photosynthesis, and molecular systematics due to their relatively conserved structure and gene content. Here, I present a comprehensive comparative analysis of complete chloroplast genomes from 20 taxonomically diverse plant species, focusing on 16 widely used barcoding genes to investigate patterns of genome structure, gene retention, codon usage bias, and phylogenetic relationships. Genome sizes ranged from ~121 kb in Marchantia polymorpha to over 160 kb in Vitis vinifera, with GC content largely conserved across species. A multi-gene Neighbor-Joining phylogenetic framework recovered major taxonomic groupings and revealed gene-specific topological differences, reflecting locus-specific evolutionary histories. Presence/absence profiling showed that 13 of the 16 barcoding genes were consistently retained across species and classified as core genes, while the remaining three exhibited more variable distributions and were considered accessory. This pattern reflects both broad conservation and lineage-specific gene loss across plastomes. Genome-wide similarity analysis revealed high identity among closely related taxa (e.g., Arabidopsis and Brassica) and greater divergence among bryophytes, gymnosperms, and angiosperms. Codon usage analysis revealed generally conserved patterns, with lineage-specific biases observed in Cucumis sativus and Brassica rapa, suggesting influences from mutational pressure and potential translational selection. This integrative analysis highlights the dynamic yet conserved nature of chloroplast genomes and underscores the value of combining multiple genomic features in plastome evolution studies. The resulting dataset and analytical pipeline offer a useful resource for future phylogenomic, evolutionary, and biodiversity research in plant science.