Leaves are three-dimensional organs that arise from the shoot apical meristem to facilitate photosynthesis. In most cases, leaves have distinct adaxial and abaxial surfaces which are specialised for light capture and gas exchange. Maintaining these domains is critical for the development of planar, leaves. But leaves also occur in a variety of shapes; they can be simple, with an undivided blade, or complex, and possess leaflets. In Arabidopsis thaliana, serrations arise due to differential growth along the edge of the leaf whereby some regions of the edge grow more than adjacent regions. Altering the timing and extent of the regions of differential growth results in different degrees of leaf margin elaboration. The BLH family of homeobox transcription factor genes in Arabidopsis thaliana redundantly contribute to the shape and frequency of leaf margin serrations. We are investigating how BLH genes affect leaf shape and the consequences of leaf shape changes on plant photosynthetic capacity and growth.