Extended differentiation of veins and stomata is essential for the expansion of large leaves in Rheum rhabarbarum.

We demonstrate that R. rhabarbarum adjusts the initiation of stomata and minor veins at high light, allowing for the production of larger leaves uncoupled from lower vein and stomatal densities. We also present evidence for an independent control of vein and stomatal initiation, suggesting that this adjustment must involve some unknown developmental mechanism.