Prickly pear cacti typically grow with flat, rounded platyclades that are armed with two kinds of spines; large, smooth, fixed spines and small, hairlike spines called glochids that easily penetrate skin and detach from the plant. Many types of prickly pears grow into dense, tangled structures.

Like all true cactus species, prickly pears are native only to the Western hemisphere; however, they have been introduced to other parts of the globe. Prickly pear species are found in abundance in Mexico, especially in the central and western regions. They are also found in the West of the United States, from arid regions in the Northwest, throughout the mid and lower elevations of the Rocky Mountains, and especially in the Southwest. Prickly pears are also the only types of cactus natively found to grow far east of the Great Plains states, as far north-east as Long Island, where it can be found in Northport.

Prickly pear species were introduced into Australia in the late 1800s, causing major ecological damage in the eastern states (see www.northwestweeds.nsw.gov.au). They are also found in the Mediterranean region of southern Europe, especially on the island nation of Malta where they grow on cactus found all over the island, and can be found in enormous numbers in parts of South Africa, where it was introduced from South America. Opuntia are the most cold-tolerant of the lowland cacti, extending into western and southern Canada; one subspecies, Opuntia fragilis var. fragilis, has been found growing along the Beatton River in central British Columbia, southwest of Cecil Lake at 56° 17’ N latitude and 120° 39’ W longitude.

Charles Darwin was the first to note that these cacti have thigmotactic anthers: when the anthers are touched, they curl over, depositing their pollen. This movement can be seen by gently poking the anthers of an open Opuntia flower.  [1]