Evolution of the Chlorophyta: Insights from chloroplast phylogenomic analyses

Green plants comprise two main clades: the Streptophyta, which include charophyte green algae and the embryophytic land plants, and the Chlorophyta including a wide diversity of marine, freshwater, and terrestrial green algae. Establishing a robust phylogeny is important to provide an evolutionary framework for comparative and functional studies. During the last two decades our understanding of the evolution of green algae has profoundly changed, first by phylogenetic analyses of nuclear ribosomal sequence data (mainly 18S), and more recently by analyses of multi-gene and chloroplast genomic data. The phylogenetic relationships among the main streptophytan lineages have been extensively studied and are now relatively well resolved. Although a lot of progress has been made in the last few years, the phylogenetic relationships in the Chlorophyta are still less well established. Here we review how chloroplast genomic data have contributed to address relationships among the main chlorophytan lineages. We highlight recent progress and conflicts among different studies, and discuss future directions in chloroplast phylogenomics of green algae.