One of the most remarkable examples of convergent evolution is the transition from C₃ to C₄ photosynthesis, an event that occurred on over 60 independent occasions. The evolution of C₄ is particularly noteworthy because of the complexity of the developmental and metabolic changes that took place. In most cases, compartmentalized metabolic reactions were facilitated by the development of a distinct leaf anatomy known as Kranz. C₄ Kranz anatomy differs from ancestral C₃ anatomy with respect to vein spacing patterns across the leaf, cell-type specification around veins, and cell-specific organelle function. Here we review our current understanding of how Kranz anatomy evolved and how it develops, with a focus on studies that are dissecting the underlying genetic mechanisms. This research field has gained prominence in recent years because understanding the genetic regulation of Kranz may enable the C₃-to-C₄ transition to be engineered, an endeavor that would significantly enhance crop productivity.

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