Organ Pipe Cactus species has several narrow stems that rise vertically, growing from a single short trunk just above the ground level. These stems are about 6 inches (15 cm) thick and grow to a height of 16 feet (5 m), however it has been known to reach 23 to 26 feet (7 to 8 m). These stems rarely branch but rather grow annually from the tip of the last growth. The mature plant can reach a width of 12 feet (3.7 m). Each stem has 12 to 19 1/3 inch (.85 cm) high ribs that bear dark brown to black spines that turn gray as it matures. It takes 150 years to reach maturity. The older plants produce three-inch (8 cm) funnel-shaped white flowers annually which are open at night and close by the morning and have a purple or pink tint to them. These usually grow during April, May, and June. The organ pipe cactus is usually pollinated by bats. The plant also produces fruit about the size of a tennis ball. Beneath the fruit's spined exterior is red flesh that supposedly tastes like watermelon. This fruit has traditionally been harvested by the Seris, who call the plant ool, and is used as a medicine
