Plants in arid environments often have predictably different phenotypes than those in moist environments. Within species, such trait–environment associations could indicate local adaptation, yet supporting evidence is rare. A new study looks at Protea repens a shrub found in the Cape Floristic Region.
Carlson et al. show both broad-scale stomatal variation and its evolutionary mechanism by combining data from a common garden with that from two wild populations. In the garden, stomatal density was higher in plants sourced from hotter, drier sites. In the wild, plants with denser stomata had higher fecundity, cooler leaves, and increased photosynthesis, but only in the drier of two sites. These findings show how stomatal density influences physiology differently among sites and uniquely demonstrates local adaptation.