Cactus plants are native to the Americas and grow throughout the western and southwestern United States, as far north as Utah and Idaho. The plant has adapted to survive in rough, inhospitable terrain with poor soil and little water and is leafless, with swollen stems and spines. Over 2,000 species exist. All of them produce blossoms and fruit, but only two--saguaro and organ pipe cactus--produce white flowers. Cacti make attractive (if thorny) landscape plants in warm, dry climates and provide habitats and food for birds and wildlife. Grow miniature varieties as houseplants.
Examine the cactus for the time of bloom. Saguaro and organ pipe cactus bloom at night, a few hours after sunset. The large, white blooms are pollinated by bees, bats and white-winged doves. These flowers are short-lived, wilting by the following afternoon.
Determine the location of the cactus. Saguaro and organ pipe cactus grow natively only in Saguaro National Park, outside of Tucson, Arizona. They may be found in landscapes throughout southern Arizona.
Inspect the cactus' growth pattern. Saguaro cacti have one main trunk that branches out into several arms. Saguaros grow to a height of 50 feet. Organ pipe cacti are similar to saguaros, but they may have five to 20 branches extending from the ground in a cluster, before forming the characteristic arms. Organ pipe cacti grow to a height of 25 feet.