Saguaro Cactus
No plant defines the American West in the popular imagination quite like the saguaro — and yet its actual range is tiny, confined to a corner of the Sonoran Desert spanning southern Arizona, western Sonora in Mexico, and a small slice of California.
Overview
The saguaro (Carnegiea gigantea) is the iconic giant cactus of the Sonoran Desert and the largest cactus in the United States. Mature saguaros reach 40-60 feet tall, weigh up to 4,800 pounds when fully hydrated, and live 150-200 years. The species is restricted to the Sonoran Desert of southern Arizona and northwestern Mexico, with marginal populations in extreme southeastern California — saguaros do not occur in any other U.S. desert despite being the popular cultural symbol of all American deserts.
Saguaros grow extraordinarily slowly. A 1-year-old seedling is the size of a pea. A 10-year-old saguaro is about 1.5 inches tall. The species typically does not begin to grow its iconic side arms until age 50-75, and arms are not produced in every year — many saguaros never grow arms at all and live their entire lives as single columns. The maximum recorded number of arms on a single saguaro is 49.
The species is dependent on nurse plants for survival as a young seedling. Saguaro seeds germinate in the shade of palo verde, mesquite, ironwood, or other desert shrubs, which protect the seedling from intense desert sun and predation. After 30-60 years, the saguaro typically outgrows and shades out its original nurse plant, leaving a giant cactus standing where the nurse plant once was.
Saguaros are essential to Sonoran Desert ecology. Gila woodpeckers and gilded flickers excavate nest cavities in saguaro trunks; the cactus seals the cavities with scar tissue, creating waterproof chambers that elf owls, screech owls, kestrels, and other species use as nests for generations after the woodpeckers leave. Saguaro flowers — the state wildflower of Arizona — bloom in May and June and provide critical nectar for lesser long-nosed bats, white-winged doves, and many native bees.
Saguaro National Park (split into two units flanking Tucson) protects significant areas of saguaro forest. The species is currently threatened by climate change, with hotter and drier conditions reducing seedling survival and increasing adult mortality, particularly in the southern portion of the range.