How to grow a leaf: Generating, maintaining, and modulating flatness

Flat leaf architecture was central to the evolutionary success of vascular plants. Leaves initiate as small thumb-shaped primordia and rapidly develop into thin, flattened laminae that optimize light capture and gas exchange for photosynthesis. The generation and maintenance of this flatness is a developmentally challenging problem that requires precise spatial and temporal coordination of growth across organ axes and functional domains. Because leaves are thin expanding structures, they are inherently prone to bending and buckling, making growth-derived mechanical conflicts one of the central components of this process. In this review, we synthesize recent advances in our understanding of how molecular patterning, tissue mechanics, and coordinated growth interact to generate, maintain, and modulate leaf flatness, and outline key open questions in laminar organ morphogenesis.