Opuntia in shallow, loose soils, such as on mountain slopes. "Opuntia" spreads into large clonal colonies, which contribute to its being considered a noxious weed in some places. Animals that eat "Opuntia" include the prickly pear island snail and "Cyclura" rock iguanas. The fruit are relished by many arid land animals, chiefly birds, which thus help distribute the seeds. "Opuntia" pathogens include the sac fungus "Colletotrichum coccodes" and Sammons' Opuntia virus. The ant "Crematogaster opuntiae" and the spider "Theridion opuntia" are named because of their association with prickly pear cacti. Like most true cactus species, prickly pears are native only to
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