Evolutionary and developmental studies of unifacial leaves in monocots: Juncus as a model system.

An important objective in evolutionary developmental biology is to understand the molecular genetic mechanisms that have given rise to morphological diversity. Leaves in angiosperms generally develop as a flattened structure with clear adaxial-abaxial polarity. In monocots, however, a unifacial leaf has evolved in a number of divergent species, in which leaf blades consist of only the abaxial identity. The mechanism of unifacial leaf development has long been a matter of debate for comparative morphologists. However, the underlying molecular genetic mechanism remains unknown. Unifacial leaves would be useful materials for developmental studies of leaf-polarity specification. Moreover, these leaves offer unique opportunities to investigate important phenomena in evolutionary biology, such as repeated evolution or convergent evolution of similar morphological traits. Here we describe the potential of unifacial leaves for evolutionary developmental studies and present our recent approaches to understanding the mechanisms of unifacial leaf development and evolution using Juncus as a model system.