Xerophyte

A xerophyte is a plant defined as capable of living in regions with low water availability, such as deserts, arid plains, and rocky mountains. The term derives from ancient Greek: 'xeros' meaning dry, and 'phyton' meaning plant.

Xerophytes do not constitute a single taxonomic group descended from one plant species. Rather, it is an ecological classification: many plants from different families have independently developed similar features because they face the same environmental stresses. A well-known example is the cactus (Cactaceae) of the Americas and the euphorbias of Africa: their appearance is similar, but their evolutionary origins are distant.

How they conserve water

The primary mechanism is reduction of water loss through transpiration and storage of water when available. Common features include small leaves or leaves replaced by spines, to minimize surface water loss; a thick waxy cuticle on the leaf surface; stomata (breathing pores) that are few in number, sunken below the surface, or open only at night; and white hairs on the surface that can trap air to reduce evaporation.

Another mechanism involves root systems. Some plants have long roots that penetrate deep to reach groundwater, while others have shallow, spreading roots to quickly capture sparse rainfall. Succulents store water in their leaves or stems.

Biochemical adaptation

Many desert plants use a photosynthetic pathway called CAM (Crassulacean Acid Metabolism). This pathway captures carbon dioxide at night when the air is cooler, then uses it during the day with stomata closed, thereby minimizing water loss per unit carbon gained. The C4 pathway also helps plants survive high heat and intense sunlight.

Classification and related terms

Xerophytes are contrasted with mesophytes (plants requiring moderate water) and hydrophytes (plants living in water). Halophytes, plants of coastal and saline soils, sometimes display features similar to xerophytes because salt also restricts plant water uptake. Other related categories include succulents and plants that complete their life cycle rapidly during the rainy season.