Saguaro Cactus (Carnegiea gigantea)
The saguaro cactus is the most thoroughly studied plant in southern Arizona's Desert. It is the largest cactus in the US, comonly reaching a height of 40 feet. The saguaro's cylindrical stem is pleated, and the ridges of the lower 8 feet are lined with clusters of hard spines. In May and June, its white flowers bloom and a month later produce juicy red fruit. The saguaro withstands the heat by waterproofing its epidermis with a waxy cuticle, which restricts water loss almost exclusively to the stomates (pores for gas exchange). Its spines also serve to reduce water loss by providing shade for the cactus. Water comprises most of the weight of the saguaro which, when fully hydrated, weighs about 80 pounds per foot. The saguaro cactus is a fascinating feature of the Arizona desert.