The Saguaro, pronounced "sah-wah-roh", (Carnegiea gigantea) is a large, tree-sized cactus species in the monotypic genus Carnegiea. It is native to the Sonoran Desert in Arizona, the Mexican state of Sonora , and an extremely small area of California. The saguaro blossom is the state flower of Arizona.

The common name of the cactus, saguaro, is a Spanish-language adaptation of a word used by a local aboriginal American nation, the Tohono O'odham, for the plant.

Saguaros have a relatively long life span. They take up to 75 years to develop a side arm. The arms themselves are grown to increase the plant's reproductive capacity (more apices equal more flowers and fruit). The growth rate of saguaros is strongly dependent on local precipitation patterns, and saguaros in drier western Arizona grow only half as fast as those in and around Tucson, Arizona. Some specimens may live for more than 150 years;[1] the champion saguaro grows in Maricopa County, Arizona and is 13.8 meters (45.3 ft) tall with a girth of 3.1 meters (10 ft). (It was injured as a result of the Cave Creek Complex fire in June 2005.) In addition to being slow growing, they are also slow to propagate. Harming one in any manner (including cactus plugging) is illegal by state law in Arizona, and when houses or highways are built, special permits must be obtained to move or destroy any saguaro affected.

The spines on smaller saguaro (having a height less than 2 meters or 6 feet) grow rapidly, up to a millimeter per day. When held up to the light or bisected, alternating light and dark bands transverse to the long axis of spines can be seen. These "transverse bands" have been correlated to daily growth (one light/dark couplet equals one day of growth). In columnar cacti, spines almost always grow from the apex of the plant and then cease to grow as they are moved to the side and the apex continues to grow upwards. Thus, the older spines are towards the base of a columnar cactus and newer spines are near the apex. Current studies are underway to examine the relationship of carbon and isotope ratios in the tissues of spines to the past climate and photosynthetic history of the plant.[2]

The night blooming flowers appear April-May and the sweet, ruby-colored fruit matures by late June. Each fruit can contain up to 2,000 seeds. Saguaro flowers are self incompatible and require a pollenizer to supply viable pollen. A well-pollinated fruit will contain several thousand tiny seeds, and large quantities of pollen are required for pollination. The major pollinators are bats, primarily the Lesser Long-nosed Bat, feeding on the nectar from the night-blooming flowers, which often remain open in the morning. The characteristics of the flower are geared toward pollination by the bats: the nocturnal opening of the flowers, maturation of pollen, and the nectar.

Gila Woodpecker, Purple Martins, House Finches, and Gilded Flicker live in holes inside saguaros. Flickers excavate larger holes higher on the stem, penetrating the ribs. Their holes sometimes cause enough damage to cause death and other problems. These woodpeckers create new nest holes each season, rather than reuse the old ones, thus leaving convenient nest holes for a variety of other animals, especially birds such as the Elf Owl.

The ribs of the saguaro were used for construction and other purposes by aboriginal Americans of the region. A fine example can be seen in the roofing of the cloisters of the Mission San Xavier del Bac on the Tohono O'odham lands near Tucson, Arizona. The Seri people of northwestern Mexico used the plant, which they call mojépe, for a number of purposes.

The saguaro is often used as a generic emblem in commercials and logos that attempt to convey a sense of the southwest, even when the product has no connection to Arizona, or the Sonoran Desert. For instance, no saguaros are found within 250 miles (400 km) of El Paso, Texas, but the silhouette is found on the label of Old El Paso brand products. Though the geographic anomaly has lessened in recent years, Western films once enthusiastically mislocated saguaros in, for example, Monument Valley of Arizona, in New Mexico, and in Texas. There are no wild saguaros anywhere in such western U.S. states as Texas, Colorado, Utah, New Mexico, or Nevada, nor in the high deserts of northern Arizona.