Plants and animals have learned to live in these unfriendly surroundings. Cacti of the Desert More than one cactus is called cacti. A cactus is a plant with a plump stem and a woody inner skeleton. When it rains, the cactus soaks up water like a sponge. Cactus plants live in harsh, dry climates where other plants that need water often cannot survive.
Cactus plants have areoles.
Areoles are small pits, or spots, from which spines grow, and sometimes tiny hairs, as well. The areoles help to keep heat out and moisture inside the plant. Saguaro-Giants of the Desert One of the largest cacti in the whole world is found in the Sonoran Desert. It is called a saguaro. It takes many years for these cacti to grow so big.