The pure white waxy blossom of the giant saguaro cactus was designated the state flower of Arizona in 1931. Saguaro cactus (Cereus giganteus) is indigenous to Arizona and grows to a height of forty to fifty feet and lives to an age of 150 to 200 years.

Native to the Sonoran Desert in the southwestern United States and northern Mexico, saguaros are slow growing and take up to 75 years to develop a side shoot. They are also slow at propagating, and saguaro cactus is a candidate for the endangered species list. Harming one in any manner is illegal in Arizona, and during construction, special precautions must be taken to move every saguaro affected.

Source:

Arizona State Symbols: Arizona State Library / Archives

Links:

State Flowers - 50 States List
National Flower