About Opuntia polyacantha var. arenaria (Engelm.) B.D.Parfitt
This taxon is a variety of the cactus Opuntia polyacantha. Opuntia polyacantha grows to a height of 10–30 centimetres (4–12 inches), and forms low, wide mats of pads that can reach 2–3 m (6+1⁄2–9+7⁄8 ft) across. Its succulent green pads are oval or circular, and can grow up to 27 cm long by 18 cm wide (10+5⁄8 by 7+1⁄8 inches). Its areoles are tipped with woolly brown fibers and glochids. Most areoles bear spines that vary widely in size, shape and color; spines range from 0.4 to 18.5 cm (1⁄8 to 7+1⁄4 in) in length, and may be stout or thin, straight or curling. Flowers develop from semi-flattened pear-shaped, spine-covered stem segments. The flowers are 2.5 to 4 cm (1 to 1+5⁄8 in) long, and can be yellow, magenta, or red, and typically turn 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 a very wide range of temperatures, surviving as low as −46 °C (−50 °F) in the Yukon Territory, Canada, and well above 38 °C (100 °F) in locations such as Chihuahua, Mexico. This cactus is native to North America, where it is widespread across western Canada, the Great Plains, the central and western United States, and Chihuahua in northern Mexico. A disjunct population was discovered in the Thousand Islands region of Ontario, Canada in 2018. It 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. New plants can grow from a displaced stem segment. Native Americans used this cactus as a medicinal plant, with different plant parts used to treat a range of symptoms. This pricklypear serves as a food source for many types of animals; it makes up over half of the winter food for black-tailed prairie dogs in one studied area. Pronghorn antelope feed on it, especially after wildfires burn off the 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 disturbed waste areas where higher quality forage cannot become established, and an abundance of this cactus is an indicator of poor-quality land. Several insect species feed on or attack this cactus: the cactus moth Melitara dentata, the blue cactus borer Olycella subumbrella, and the cactus bug Chelinidea vittiger. Opuntia polyacantha was both admired and complained about by members of the Lewis and Clark Expedition. When the skin and seeds are removed, its fruit can be eaten raw or made into candy.
