A beautiful silhouette of the Saguaro cactus at sunset.
The Saguaro Cactus, is composed of a tall, thick, fluted, columnar stem, 18 to 24 inches in diameter, often with several large branches (arms) curving upward in the most distinctive conformation of all Southwestern cacti.
The skin is smooth and waxy, the trunk and stems have stout, 2-inch spines clustered on their ribs. When water is absorbed , the outer pulp of the Saguaro can expand like an accordion, increasing the diameter of the stem and, in this way, can increase its weight by up to a ton.
The Saguaro often begins life in the shelter of a "nurse" tree or shrub which can provide a shaded, moister habitat for the germination of life. The Saguaro grows very slowly -- perhaps an inch a year -- but to a great height, 15 to 50 feet. The largest plants, with more than 5 arms, are estimated to be 200 years old. An average old Saguaro would have 5 arms and be about 30 feet tall.