Evolution of Primitive Land Plants: A Review

Our understanding of the evolution of primitive land plants is overviewed. Molecular phylogenetic data suggest that the suggested ancestor of the land plants is Charophyceae, although other ancestry is suggested based on different lines of evidence. Invasion to land environment during the mid-Ordovician or earlier should have been made possible by chemical compounds, ozone, flavonoid, cutin, sporopollenin, and lignin, against UV irradiation, drought and gravity. Recent molecular analyses with large data sets and fossil data provide robust evidence on land plant evolution and phylogeny, but the deep relationship of land plants is still unclear. It is likely that the earliest land plants are liverwort-like, and pteridophytes are biphyletic while seed plants are monophyletic. Evolutionary innovations, such as the appearance of different heteromorphic alternation of generations, sporophyte apical meristem, polysporangiate sporophyte, vascular tissue, leaf (microphyll and megaphyll), and seed, have been increasingly understood not only by paleobotanical, comparative morphological, biochemical, and developmental studies, but also by recent molecular genetic analyses.