Sauaro cactus (Carnegiea gigantea)

Anatomy and Adaptations: Cacti have many adaptations that allow them to live in dry areas; these adaptations let the plant collect water efficiently, store it for long periods of time, and conserve it (minimizing water loss from evaporation).

Cacti have a thick, hard-walled, succulent stem - when it rains, water is stored in the stem. The stems are photosynthetic, green, and fleshy. The inside of the stem is either spongy or hollow (depending on the cactus). A thick, waxy coating keeps the water inside the cactus from evaporating.

Prickly Pear cactus (genus Opuntia)

Many cacti have very long, fibrous roots, which absorb moisture from the soil. Some, like ball cacti, have shorter, more compact roots that absorb dew water that falls off the cactus.

Instead of leaves, most cacti have spines or scales (which are modified leaves). These spines and scales do not lose water through evaporation (unlike regular leaves, which lose a lot of water). The spines protect the cactus from predators (animals that would like to eat the cactus to obtain food and/or water). Areoles are circular clusters of spines on a cactus. Flowers bud at an areole and new stems branch from an areole.

Reproduction: Cacti are flowering plants. The flowers produce seed-bearing fruit. Many cactus species are pollinated by bats. The delicate flowers usually bloom for a short period of time in the Spring.

Many cacti can also be grown from broken-off parts of the plant (but the new plant will be genetically identical to the original plant).

Habitat and Range: Cacti are native to the Americas (North and South America). They are generally found in dry areas, but can be found in many habitats (temperate, sub-tropical, and tropical), ranging from deserts to tropical rainforests to high in the Andes Mountains.

Related Pages:

Desert Animals Desert animals are adapted to a scarcity of water, extreme temperatures, and non-abundant food.

Deserts of the World Label the major deserts of the world. Answers

References:
Cactaceae from Texas A. and M.
Cactus Illustrations from the Smithsonian Institution