About Opuntia polyacantha Haw.
Opuntia polyacantha Haw. is a prickly pear cactus that grows 10 to 30 centimeters (4 to 12 inches) tall, forming low mats of pads that can reach 2 to 3 meters (6 1/2 to 9 7/8 feet) wide. Its succulent green pads are oval or circular, growing up to 27 by 18 centimeters (10 5/8 by 7 1/8 inches) in size. The cactus's areoles are tipped with woolly brown fibers and glochids; many areoles bear spines that are highly variable in size, shape, and color, ranging from 0.4 to 18.5 centimeters (1/8 to 7 1/4 inches) long, and can be stout or thin, straight or curling.
Flowers develop from spine-covered, semi-flattened pear-shaped stem segments. The flowers themselves are 2.5 to 4 centimeters (1 to 1 5/8 inches) long, and can be yellow, magenta, or red, fading to pink or orange as they age. The fruit is cylindrical, brownish, dry, and spiny. This cactus reproduces via seed, layering, and re-sprouting from detached stem segments. Across its natural range, it tolerates an extremely broad range of temperatures, surviving as low as −46 °C (−50 °F) in Canada's Yukon Territory, and well above 38 °C (100 °F) in regions like Chihuahua, Mexico.
It is native to North America, with a widespread distribution across western Canada, the Great Plains, the central and western United States, and Chihuahua in northern Mexico. In 2018, a separate disjunct population was discovered in Ontario, Canada's Thousand Islands region. This cactus grows in a wide variety of habitat types, including sagebrush, Ponderosa pine forest, prairie, savanna, shrublands, shrubsteppe, chaparral, pinyon-juniper woodland, and scrub. Individual plants typically grow best in sandy soil, and new plants can develop from a single displaced stem segment.
Native Americans used this species as a medicinal plant, with different plant parts used to treat a range of symptoms. The cactus provides food for many types of animals; in one area, it makes up over half of the winter diet of black-tailed prairie dogs. Pronghorn antelope feed on it, especially after wildfires burn off its spines. When little other food is available, ranchers intentionally burn stands of this cactus to make it edible for livestock. It will also grow in waste areas where high-quality forage cannot grow, and an abundance of this cactus is an indicator of poor-quality land.
Several insect species target this cactus, including the cactus moth Melitara dentata, the blue cactus borer Olycella subumbrella, and the cactus bug Chelinidea vittiger. The Lewis and Clark Expedition encountered O. polyacantha, sometimes admiring it but more often complaining about the plant. When the skin and seeds are removed, the fruit can be eaten raw or processed into candy.
