Cereus giganteus

The dominant plant of the Tucson area and the symbol of the State of Arizona. This cacti towers over 40ft (12m) over the desert, sometimes a lone sentinel, or often thick stands creating a cacti forest. The Saguaro defines the upper Sonoran Desert both to the scientist and the layman.

The saguaro is surprisingly fragile for such a large plant. The seedling saguaro must start in a spot sheltered from the desert sun, which can heat the ground surface to over a deadly 150 degrees F (65 degrees C). The shade of a "nurse plant" or a rock provides the usual location. Without this protection the saguaro seedling would probably not survive. The saguaro will the grow many years as a straight pole. A few decades later the first arms might appear. A mature, multi armed saguaro might live several centuries. Frost, lightning and man are the primary dangers to a mature
saguaro. The saguaro grows only at the tip of the stem or arm, if this tip is killed by frost or lightning that stem will stop growing, though more branches usually sprout when this happens.

Taken from Andrew Cooper's cactus website