Prickly pear cactus

Prickly pears typically grow with flat, rounded cladodes (also called platyclades) that are armed with two kinds of spines; large, smooth, fixed spines and small, hairlike prickles called glochids, that easily penetrate skin and detach from the plant. Many types of prickly pears grow into dense, tangled structures.
In the 1930s, the prickly pear was considered to be the worst plant invader in South Africa, particularly in the Eastern Cape. 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 Western United States, in arid regions in the Northwest, throughout the mid and lower elevations of the Rocky Mountains such as in Colorado, where species such as Opuntia phaeacantha, Opuntia polyacantha and others become dominant, and especially in the desert Southwest. Prickly pears are also the only types of cactus found to grow natively far east of the Great Plains states; O. humifusa is widespread throughout southern New England and Long Island, where it can be found in Northport, as well as throughout the northern Great Lakes states and southern Ontario, Canada. O. humifusa is also a prominent feature of the flora at Illinois Beach State Park, in Winthrop Harbor, Illinois, north of Chicago, and of Indiana Dunes State Park southeast of Chicago. (information from Wikipedia)