Transport efficiency through uniformity: organization of veins and stomata in angiosperm leaves

Leaves of vascular plants use specific tissues to irrigate the lamina (veins) and to regulate water loss (stomata), to approach homeostasis in leaf hydration during photosynthesis. As both tissues come with attendant costs, it would be expected that the synthesis and spacing of leaf veins and stomata should be coordinated in a way that maximizes benefit to the plant. We propose an innovative geoprocessing method based on image editing and a geographic information system to study the quantitative relationships between vein and stomatal spatial patterns on leaves collected from 31 angiosperm species from different biomes. The number of stomata within each areole was linearly related to the length of the looping vein contour. As a consequence of the presence of free-ending veinlets, the minimum mean distance of stomata from the nearest veins was invariant with areole size in most of the species, and species with smaller distances carried a higher density of stomata. Uniformity of spatial patterning was consistent within leaves and species. Our results demonstrate the existence of an optimal spatial organization of veins and stomata, and suggest their interplay as a key feature for achieving a constant mesophyll hydraulic resistance throughout the leaf.