Stomata are microscopic pores formed by specialized cells in the leaf epidermis and permit gaseous exchange
between the interior of the leaf and the atmosphere. Stomata in most plants are separated by at least one epidermal
pavement cell and, individually, overlay a single substomatal cavity within the leaf. This spacing is thought to enhance
stomatal function. Yet, there are several genera naturally exhibiting stomata in clusters and therefore deviating from
the one-cell spacing rule with multiple stomata overlaying a single substomatal cavity. We made use of two Begonia
species to investigate whether clustering of stomata alters guard cell dynamics and gas exchange under different
light and dark treatments. Begonia plebeja, which forms stomatal clusters, exhibited enhanced kinetics of stomatal
conductance and CO2 assimilation upon light stimuli that in turn were translated into greater water use efficiency.
Our findings emphasize the importance of spacing in stomatal clusters for gaseous exchange and plant performance
under environmentally limited conditions
