Being stingy with resources

Some leaves have made changes as they evolved in order to conserve resources. The blade of these leaves, for instance, has completely disappeared: only the petiole remains, and over time it has expanded into a phyllode (An expanded leaf-like petiole taking on the function of a leaf blade.
). The leaf is the tree's biggest user of water; by eliminating the blade and retaining only the petiole, the tree minimizes its water losses. This adaptation is especially valuable in trees that grow in arid climates – when every drop of water counts, transpiration must be carefully controlled.