Leaf evolution: integrating phylogenetics, developmental dynamics, and genetic insights across land plants

The acquisition of leaves represented a pivotal innovation in plant evolution, enabling more efficient photosynthesis and providing a foundation for the development of increasingly three-dimensional and morphologically diverse organisms. Paleobotanical studies have revealed that leaves did not arise from a single common origin; rather, they evolved multiple times independently during the diversification of land plants. Despite these insights, the precise evolutionary trajectories leading to leaf formation remain unclear. Reconstructing the evolutionary history of leaves requires a robust phylogenetic framework, a detailed understanding of leaf developmental processes across different plant lineages, and elucidation of the underlying molecular mechanisms. Recent advances in high-throughput (HT) sequencing technologies have dramatically accelerated progress in these areas, offering insights that were unattainable just a decade ago. The widespread availability of HT sequencing has also encouraged researchers to expand their focus beyond traditional model species, thereby promoting a broader appreciation of the evolutionary processes underlying diverse plant traits, including leaf evolution. In this review, we focus on the current understanding of leaf evolution by integrating phylogenetic relationships, the developmental dynamics of the shoot apical meristem - the site of leaf initiation - and comparative analyses of leaf morphogenesis in the context of key regulatory genes across plant lineages.