(Carnegiea gigantea), cactus species of the family Cactaceae, native to Mexico and to Arizona and California in the United States.

Ribbed and columnar when young, a saguaro usually develops five or six branches at a height of about 5 metres (16 feet). Slow growing at first—it reaches only 2 cm (less than 1 inch) in height during its first 10 years—it grows approximately 10 cm (4 inches) a year after attaining a height of 2 to 3 metres (about 6.5 to 10 feet). It blooms for the first time when it is 50 to 75 years old. Mature saguaros may reach 15 metres (almost 50 feet) in height. They may die at 150 to 200 years of age, most commonly by being uprooted by wind or washouts. The shallow, wide-ranging roots, adapted to gathering moisture from a large area of desert, must sometimes support up to 9,000 kg (10 tons) of top growth.

The white, night-blooming flowers, on top of trunk and branches, remain open part of the next day. The red fruits are an important food of American Indians, who also use the woody saguaro skeletons.