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.
[Illustration: Sparse, very dry, single species vegetation in Death
Valley, California.]
[Illustration: Vegetation amidst the desert pavement of the Sonoran
Desert (photograph by John Olsen).]
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.