The desert is a harsh, unforgiving environment. It is just as hazardous to plants as it is to animals. Temperatures swing wildly between extremes in desert climates. Water is scarce, and in some deserts as much as a year can elapse between rainfalls. Deserts tend to lack shade, and because there is so little humidity in the air, much more solar radiation is found in deserts than in other climates. This is too much sunlight for most plants to handle. Desert plants have found a variety of ways to cope with these extreme conditions, and survive where other plants cannot.
Smaller Leaves and Stems
One of the chief adaptions of plant life to desert climates has been to reduce leaf and stem size. This allows the plant to concentrate its water instead of spreading it out over a wider surface area. Desert trees and shrubs tend to be short, with fewer leaves and branches. The most extreme form of this adaptation is found in the cacti, whose stems and leaves have been reduced so much that only spines remain. These spines also can shade the plant, helping it conserve even more moisture. With cacti, the primary photosynthetic activity has been moved to the stalk, the main body of the plant, and away from the leaves.
Some plants in the desert have developed the ability to store water. Desert plants with thick leaves and stems are able to absorb water when it rains and continue growing even when rainfall is absent. Some desert plants have developed holding sacks in their stems that swell to hold water during those times when it is available. Some types of cactus have this ability, as do black sage and rice grass.
Other plants have learned to go dormant when water is scarce. This conserves their resources during times of hardship. When water again becomes available, these plants wake up and resume growing. Desert plants with dormant phases include lichen, moss, algae and ferns.
Some desert plants survive by only becoming fully active at night. During the night time, evaporation is least likely to occur because it is no longer so hot. Some plants, such as the yucca, turpentine bush, and brittlebush, only open their stomas at this time. Stomas are microscopic openings in the "skin" of the plant that allow it to breathe. By only exposing their mist insides to the outside air at night, they lose less moisture.