Xeromorphism

the morphological and anatomical adaptations characteristic of xerophytes—plants that grow in arid places. These adaptations include a decrease in leaf surfaces, small cells, a large number of small stomata, a dense network of veins, pubescent leaves, a waxy coat, and submerged stomata. Xeromorphism is frequently associated with the loss of leaves and their replacement with photosynthetic branches, such as cladophylls or thorns (for example, in cacti). Each of these adaptations decreases the intensity of transpiration (especially cuticular transpiration) and helps protect the plant from dehydration.

The degree of xeromorphism may vary sharply in the same plant, depending on various conditions of its environment. Xeromorphism is most pronounced in plants found in open, sunny habitats. The uppermost leaves of such plants as the sunflower are subjected to more intensive metabolic processes and transpiration than the leaves located lower on the plant; thus, the top leaves are marked by a higher degree of xeromorphism. Xeromorphism, especially microcellularity, fosters toleration of dehydration and is especially characteristic of plants that have undergone preplanting hardening to drought (although the surface area of their leaves is usually great). Xeromorphism also arises when there is a deficiency of nitrogen feeding, which, however, is not related to the increased drought-resistance of the plants.