Currently, only prickly pears (also known as nopal or nopales, from the Nahuatl word nōpalli for the pads, or nostle, from the Nahuatl word nōchtli for the fruit; see below) are included in this genus of about 200 species distributed throughout most of the Americas. Chollas are now separated into the genus Cylindropuntia, which some still consider a subgenus of Opuntia. Austrocylindropuntia, Corynopuntia and Micropuntia are also often included in the present genus, but like Cylindropuntia they seem rather well distinct. Brasiliopuntia and Miqueliopuntia are closer relatives of Opuntia.
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.
Prickly pear species are found in abundance in the West and Southwest of the United States and throughout much of Mexico. Prickly pears are also the only types of cactus natively found to grow in the eastern United States. 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. 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. The same trait has evolved convergently in other cacti (e.g. Lophophora).
The fruit of prickly pears, commonly called cactus figs, Indian fig or tuna, is edible, although it has to be peeled carefully to remove the small spines on the outer skin before consumption. If the outer layer is not properly removed, glochids can be ingested causing discomfort of the throat, lips, and tongue as the small spines are easily lodged in the skin. Native Americans like the Tequesta would roll the fruit around in suitable medium (e.g. grit) to "sand" off the glochids. Today, parthenocarpic (seedless) cultivars are also available.
Opuntia ficus-indica has been introduced to Europe and flourishes in areas with a suitable climate, such as the south of France, southern Italy, Sicily where they are referred to as fichi d'India or ficurinnia (Indian figs), along the Struma River in Bulgaria, in Southern Portugal and Madeira where they are called tabaibo or "Indian figs", and eastern and southern Spain as well as Gibraltar where they are known as chumbo or higo chumbo ("chumbo fig"). In Greece it grows in such places as Corfu and its figs are known as frangosyka (French figs) or pavlosyka (Paul's figs). The figs are also grown in Cyprus, where they are known as papoutsosyka (shoe figs). The prickly pear also grows widely on the islands of Malta where it is enjoyed by the Maltese as a typical summer fruit (known as bajtar tax-xewk, literally 'spiny figs') as well as being used to make the popular liqueur known as Bajtra. The prickly pear is so commonly found in the Maltese islands that it is often used as a dividing wall between many of Malta's characteristic terraced fields in place of the usual rubble walls. The prickly pear was introduced to Eritrea during the period of Italian colonisation between 1890 and 1940. It is locally known there as Beles and is abundant during the months of late summer and early autumn (late July - September). The Beles from the holy monastery of 'Bizen is said to be particularly sweet and juicy.
In Egypt, Saudi Arabia and other parts of the Middle East, prickly pears of the yellow and orange varieties are grown by the side or farms, beside railway tracks and other otherwise non-cultivable land. It is sold in summer by street vendors and is considered a nice refreshing fruit for that season.
Tungi is the local St. Helenian name for cactus pears. The plants (Indian Fig Opuntia) were originally brought to the island by the colonial ivory traders from East Africa in the 1850s. Tungi cactus now grows wild and organically in the dry coastal regions of the island. Three principal cultivars of tungi grow on the island: the 'English' with yellow fruit; the 'Maderia' with large red fruit; and the small firm 'Spiny Red'.
The young stem segments, usually called nopales, are also edible in most species of Opuntia. They are commonly used in Mexican cuisine in dishes such as huevos con nopales (eggs with nopal), or tacos de nopales. Nopales are also an important ingredient in New Mexican cuisine.
Most species of Opuntia contain a range of alkaloids in ample quantities, notably substituted phenethylamines. While the mere presence of such compounds has been confirmed in many species without further details, they have been studied more thoroughly in others. Identified compounds of medical significance include 3-methoxytyramine, candicine, hordenine, N-methyltyramine and tyramine.
The stem of certain Opuntia spp. can be used to treat type II diabetes, diarrhea, and stomach ache. However, usefulness of Opuntia in treating diabetes is not at all resolved. Although some researchers have shown a blood glucose-lowering effect of O. streptacantha, another study of three other species of Opuntia (O. lasiacantha, O. velutina, and O. macrocentra) showed no such effect. Yet another study, on O. megacantha, raised concern about toxic effects on the kidney.
It may be that certain species are effective and useful in diabetes while others are not but this needs to be clarified with further research before recommending its use. Furthermore, when buying nopal in the market, it is impossible to know which species one is buying and therefore whether or not it is useful in treating diabetes.
Indian Fig Opuntia (and probably others) might have a reducing effect on alcohol hangover by inhibiting the production of inflammatory mediators. Studies have yielded differing results, with some studies witnessing significant reductions in nausea, dry mouth, and loss of appetite as well as less risk of a severe hangover, while others witnessing no compelling evidence for effects on alcohol hangover.
In Mexico and the Southwest, its pulp and juice have been used to treat a numerous amount of maladies such as wounds and inflammations of the digestive and urinary tracts.
Opuntia is also added sometimes to the entheogenic drink Ayahuasca. Psychoactive compounds and derivates thereof have been confirmed in some species. These include 3,4-DMPEA, 4-hydroxy-3,5-DMPEA, and mescaline.
Cochineal is primarily used as a red food colouring and for cosmetics. The cochineal dye was used by the Aztec and Maya peoples of Central and North America. Produced almost exclusively in Oaxaca, Mexico by indigenous producers, cochineal became Mexico's second most valued export after silver. The dyestuff was consumed throughout Europe and was so highly valued that its price was regularly quoted on the London and Amsterdam Commodity Exchanges.
In present times, the highest production of cochineal is by Peru, the Canary Islands and Chile. Current health concerns over artificial food additives have renewed the popularity of cochineal dyes, and the increased demand is making cultivation of the insect an attractive opportunity in other regions, such as in Mexico where cochineal production had declined again due to the scale insect having numerous natural enemies.
Apart from cochineal, the red dye betanin can be extracted from some Opuntia plants themselves.
The 1975-1988 version of the coat of arms of Malta also featured an opuntia.
The cactus lends its name to a song by British Jazz/Classical group Portico Quartet.
Prickly pears (mostly Opuntia tomentosa) were imported into Australia in the 19th century for use as a natural agricultural fence and in an attempt to establish a cochineal dye industry. They quickly became a widespread invasive weed, rendering 40,000 km² of farming land unproductive. The moth Cactoblastis cactorum from South America, whose larvae eat prickly pear, was introduced in 1925 and almost wiped out the population. This case is sometimes cited as an example of successful biological pest control.
The same moth, introduced accidentally further north of its native range into southern North America, is causing serious damage to some native species in that area.
Other animals that eat Opuntia include the Prickly pear island snail and Cyclura rock iguanas. The fruit are relished by many aridland 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 for their association with prickly pear cacti.