Opuntia macrorhiza or gravelly soils. It is one of the shorter species of the genus, rarely over 30 cm (1 foot) tall, spreading horizontally and forming large clumps. Flowers are showy and bright yellow, sometimes with red markings near the base of the petals. Fruits are narrow, red, juicy and edible. Several varieties have proposed within the species. More study is needed to determine whether these should continue to be recognized as varieties, elevated to species status, or regarded as mere synonyms. Opuntia macrorhiza Opuntia macrorhiza is a common and widespread species of cactus with the common names plains prickly pear or
Opuntia arenaria strongly deflexed and much shorter. Overall, plants (clumps) of cladodes may be 20–30 cm across and about 4–8 cm tall. Fruits are small, about 2.5 cm. Opuntia arenaria Opuntia arenaria was considered a variety of "O. polyacantha" by many botanists, and is still treated that way in the Flora of North America. However, "O. arenaria" is diploid and "O. polyacantha" is tetraploid. It was described by Engelmann in 1856. "Opuntia arenaria" can grow in soil that is essentially pure sand. It has rhizomes up to 1.5 m long that give rise to above ground shoots with small cladodes that are