Macro shot of saguaro cactus thorns, they can reach up to 3 inches in length.
Saguaros have a relatively long life span. They take up to 75 years to develop a side arm. The arms themselves are grown to increase the plant's reproductive capacity (more apices equal more flowers and fruit). The growth rate of saguaros is strongly dependent on precipitation; saguaros in drier western Arizona grow only half as fast as those in and around Tucson, Arizona. Some specimens may live for more than 150 years (Wikipedia).