Saguaro Cactus: commonly grow to 40' tall or more and may be branched (called saguaro "arms") or unbranched. May live over 200 years and grow to heights over 75 feet; commonly begin to flower at the age of 55 (about 8' tall) and grow arms when they are between 50 and 100 years old. Their pleated stems allow them to expand and contract as they store and use up their water.