It is native to the Sonoran Desert in Arizona, the Mexican state of Sonora, and the Whipple Mountains and Imperial County areas of California.

Their sweet red fleshed fruits are turned into syrup by native peoples, such as the Tohono Oʼodham and Pima.

[7][8] The growth rate of this cactus is strongly dependent on precipitation; saguaros in drier western Arizona grow only half as fast as those in and around Tucson.

[9] Since 2014,[update] the National Register of Champion Trees listed the largest known living saguaro in the United States in Maricopa County, Arizona, measuring 13.8 m (45 ft 3 in) high with a girth of 3.1 m (10 ft 2 in); it has an estimated age of 200 years and survived damage in the 2005 Cave Creek Complex Fire.

[citation needed] As a cactus, it uses crassulacean acid metabolism photosynthesis, which confers high levels of water-use efficiency.

While the ribs of dead plants are not protected by the Arizona native plant law, the Arizona Department of Agriculture has released a memo discussing when written permission is needed before harvesting them because of the importance of the decomposition of cactus remains in maintaining desert soil fertility.

A 2007 study examined the relationship of carbon and oxygen isotope ratios in the tissues of spines of an individual to its climate and photosynthetic history (acanthochronology).

Their long, unbarbed nature means that partially embedded spines can be easily removed, but their relative length can complicate injuries.

[24] The white, waxy flowers appear in April through June, opening well after sunset and closing in midafternoon.

This pollen is produced by the extremely numerous stamens, which in one notable case totaled 3482 in a single flower.

Several floral characteristics are geared toward bat pollination (chiropterophily): nocturnal opening of the flowers, nocturnal maturation of pollen, very rich nectar, position high above ground, durable blooms that can withstand a bat's weight, and fragrance emitted at night.

[29] The ruby red fruits are 6 to 9 cm (2+1⁄2 to 3+1⁄2 in) long and ripen in June, each containing around 2000 seeds, plus sweet, fleshy connective tissue.

Seeds must wait 12–14 months before germination; lack of water during this period drastically reduces seedling survival.

Like several other highly specialized plant taxa, such as the carnivorous Genlisea and parasitic Cuscuta, the saguaro has lost the ndh plastid genes, which codes for production of NADPH dehydrogenase pathway, but unlike those taxa, the saguaro remains fully autotrophic; i.e. it does not eat or steal part of its food.

[7] The first description of the species was made by William H. Emory in 1848, during his surveys along the pre-Gadsden Purchase United States-Mexican border.

[36] This description allowed cactus expert George Engelmann to formally name it, during his work on the United States and Mexican Boundary Survey, published in 1859.

[37] The next major taxonomic treatment came from The Cactaceae, the seminal work on cactus by Nathaniel Lord Britton and Joseph Nelson Rose.

[42] Elevation is a limiting factor to its environment, as the saguaro is sensitive to extended frost or cold temperatures.

[8] No confirmed specimens of wild saguaros have been found anywhere in Nevada, New Mexico, Texas, Colorado, Utah, nor in the high deserts of northern Arizona.

[46] Gila woodpeckers and gilded flickers create holes in the cactus to make nests, which are later used by other birds, such as elf owls, purple martins, and house finches.

[47][48][a][49][b][50] Gilded flickers excavate larger holes higher on the stem compared to Gila woodpeckers.

[53][54] Harming or vandalizing a saguaro in any manner, such as shooting them (sometimes known as "cactus plugging")[55] is illegal by state law in Arizona.

[57] This is common when the cactus falls over in a storm, its location interferes with a house addition, or it becomes a potential hazard to humans.

[61] Invasive species, such as buffelgrass and Sahara mustard, pose significant threats to the Sonoran Desert ecosystem by increasing the rate of fires.

[15] The utility of the saguaro is well known to Native Americans such as the Tohono O'odham, Pima, and Seri peoples, who still use nearly every part of the plant.

[47] The Tohono O'odham use long sticks to harvest the fruits, which are then made into a variety of products, including jams, syrups, and wine.

A pair of saguaro ribs, about 6 m (20 ft) long, are bundled together to make a harvesting tool called a kuibit.

[21]: 324–326  At the end of the harvest, each family would contribute a small amount of syrup to a communal stock that would be fermented by the medicine man.

[68][43] Though the geographic anomaly has lessened in recent years,[citation needed] Western films once enthusiastically placed saguaros in the Monument Valley of Arizona (north of their native range), as well as New Mexico, Utah, and Texas.

America West Airlines, and later U.S. Airways after their merger in 2007, used the call sign "CACTUS" for radio communication on flights.