Most desert plants are drought- or salt-tolerant. Some store water in their leaves, roots, and stems. Other desert plants have long tap roots that penetrate the water table, anchor the soil, and control erosion. The stems and leaves of some plants lower the surface velocity of sand-carrying winds and protect the ground from erosion.
Deserts typically have a plant cover that is sparse but enormously diverse. The Sonoran Desert of the American Southwest has the most complex desert vegetation on Earth. The giant saguaro cacti provide nests for desert birds and serve as "trees" of the desert. Saguaro grow slowly but may live 200 years. When 9 years old, they are about 15 centimeters high. After about 75 years, the cacti are tall and develop their first branches. When fully grown, saguaro are 15 meters tall and weigh as much as 10 tons. They dot the Sonoran and reinforce the general impression of deserts as cacti-rich land.
Although cacti are often thought of as
characteristic desert plants, other types of plants have adapted well to
the arid environment. They include the pea family and sunflower family.
Cold deserts have grasses and shrubs as dominant vegetation.
 Sparse, very dry, single-species vegetation in Death Valley, California. |
 Vegetation amidst the desert pavement of the Sonoran Desert (Photograph by John Olsen.) |
Information provided by A . S . Walker
http://pubs.usgs.gov