Opuntia

• 1. Introduction

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  Opuntia is a genus of flowering plants in the cactus family Cactaceae, and most people know it as the prickly pear. Cacti are native to the Americas and suited to arid climates, though shifts in rainfall and temperature driven by climate change still threaten them. Even so, the prickly pear has travelled to Australia, southern Europe, the Middle East and parts of Africa. Wherever it lands, it seems to earn a strong reputation. Some people welcome it as food, and others fight it as a pest. How can one plant be both? What does a thorny cactus have to do with the way nations and peoples describe themselves? And what do its many names reveal about the hands it has passed through?

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• 2. Pads and Prickles

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  A fully grown Opuntia ficus-indica can develop a trunk about 1 metre thick beneath a crown more than 3 metres across. The green to blue-green pads on this species are called cladodes. Many bear a few spines of up to 2.5 centimetres, and some have no spines at all.

  The flat, rounded pads of the genus, sometimes called platyclades, carry two kinds of defence. The obvious kind is the large, smooth, fixed spine. The subtler kind is the glochid, a small hairlike prickle that clings to skin or hair and then detaches from the plant.

  Habit varies greatly across the genus. Most prickly pears are shrubs, but O. galapageia of the Galápagos grows as a tree.

  Opuntia flowers are large and usually solitary, and they are bisexual, with numerous stamens in spiral or whorled clusters. The tepals are distinct and spirally arranged. The fruit that follows is a berry holding seeds with arils, and it can be red, wine-red, green or yellow-orange.

  Chemists studying Opuntia have found polyphenols, dietary minerals and betalains in varying amounts. Gallic acid, vanillic acid and catechins are among the compounds identified in basic research. In O. ficus-indica, the betalains betanin and indicaxanthin reach their highest levels in the fruit.

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• 3. Names and Kin

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  In 1753, Carl Linnaeus published Species Plantarum, the work that botanists treat as the starting point of modern plant naming. He placed every cactus he knew in a single genus, Cactus. In 1754, the Scottish botanist Philip Miller divided that group into several genera, Opuntia among them. He told them apart mainly by the form of their flowers and fruits.

  The genus takes its name from Opus, a city of Ancient Greece. Common names are far more tangled. Prickly pear can mean the fruit, the plant, or both. Spanish speakers say tuna for the fruit and nopal for the pads, with the plural nopales. Nopal comes from the Nahuatl word nōpalli. Nostle, another name for the fruit, comes from the Nahuatl nōchtli. Sabra, sabbar and paddle cactus are further names for the plant.

  Sorting the species is hard because Opuntia hybridizes readily. That produces a reticulate phylogeny, a family tree in which branches merge as well as split. The genus also tends toward polyploidy. The ancestral diploid state is 2n=22, but many species are hexaploid, 6n=66, or octaploid, 8n=88. Botanists now use DNA sequencing to define and separate species, and names have been coined for variants and subtypes within them.

  Several groups once placed in Opuntia now sit elsewhere, including Austrocylindropuntia, Brasiliopuntia, Corynopuntia, Micropuntia and Miqueliopuntia. Disocactus phyllanthoides was once filed as O. speciosa. The chollas, now recognized in the separate genus Cylindropuntia, have cylindrical stem segments instead of flat ones, armed with large barbed spines.

  The jumping cholla, C. fulgida, has very brittle young stems. They snap off when the barbed spines catch on clothing or animal fur, and this is how the plant reproduces vegetatively. The spines can stay embedded in skin, causing discomfort and sometimes injury.

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• 4. Native Ground and Wildlife

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  Mexico, one of the ancient homes of the cactus pear, has prickly pears in abundance, especially in its central and western regions. They are equally at home on the Caribbean islands known as the West Indies.

  In the western and south central United States, species such as O. phaeacantha and O. polyacantha have become dominant across the lower elevations of the Rocky Mountains and the southern Great Plains. Several types are endemic to the desert Southwest.

  On the East Coast, sandy beach scrub from Florida to southern Connecticut is home to O. humifusa and O. stricta. These two, together with O. pusilla, are found from the East Coast south into the Caribbean and the Bahamas. Inland, the eastern prickly pear grows on midwestern sand prairies near the Mississippi, Illinois and Ohio rivers. It also occurs in the hilly parts of southern Illinois and in sandy or rocky parts of northern Illinois.

  Of all the lowland cacti, Opuntia species are the most cold-tolerant, and they reach western and southern Canada. One variety, O. fragilis var. fragilis, grows along the Beatton River in north-eastern British Columbia, southwest of Cecil Lake, at 56° 17' N. Others live in the Kleskun Hills Natural Area of north-west Alberta, at 55° 15' N.

  On the Galápagos Islands, O. galapageia was once treated as a number of separate species. It is now divided only into varieties and subvarieties. Most are confined to one or a few islands, and they have been described as an excellent example of adaptive radiation. Islands with tall, trunked varieties are also home to giant tortoises, while islands without tortoises have low or prostrate forms. Because tortoises rely on the cactus as a prime food, it plays an important part in the food web.

  Charles Darwin was the first to notice that these cacti have thigmotactic anthers. When touched, the anthers curl over and deposit their pollen on the visiting pollinator. The movement can be seen by gently poking the anthers of an open flower. The same trait evolved independently in other genera, such as Lophophora.

  Bees pollinate most Opuntia species. The bee genera Diadasia and Lithurgus include specialists that visit Opuntia exclusively. Only a few species, such as O. cochenillifera and O. stenopetala, are pollinated by hummingbirds.

  Many arid-land animals relish the fruit, chiefly birds, which help spread the seeds. Antelopes, nonhuman primates, elephants and humans also scatter them. For elephants the price is high, because the plant's sharp parts harm the mouth, stomach and intestines. Other animals that eat Opuntia include the prickly pear island snail and Cyclura rock iguanas. Its pathogens include the sac fungus Colletotrichum coccodes and Sammons' Opuntia virus. The ant Crematogaster opuntiae and the spider Theridion opuntia both carry names that record their association with the cactus.

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• 5. Green Hell

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  Opuntia ficus-indica thrives where winters are mild, a long dry spell is followed by hot summers with occasional rain, and humidity stays low. Its shallow root system lets it grow in thin, loose soils, even on mountain slopes. It also spreads into large clonal colonies. These traits help explain why it counts as a noxious weed in some places, and why the prickly pear is considered invasive in Australia, Ethiopia, South Africa and Hawaii, among other locations.

  Prickly pears, mostly O. stricta, were first imported into Europe during the 16th century. In South Africa they arrived from South America, and they now grow in enormous numbers in parts of that country.

  South Africa classes many Opuntia species as Category 1 invaders, among them O. aurantiaca, O. ficus-indica, O. stricta and O. tomentosa. The target is national eradication, and most activities are prohibited, including importing, propagating, introducing, moving and trading the plants. Invasive prickly pears have been found to harm the beetle population in Kruger National Park. Widespread invasions also alter the soil.

  In 1788, the founding governor of the New South Wales colony, Arthur Phillip, and the earliest European colonists are credited with the first prickly pears in Australia. The plants came from Brazil to Sydney and were most likely O. monacantha, a variety that never spread beyond the east coast. In the mid-19th century, a number of other types reached Australian gardens. Settlers used the cactus as agricultural fencing and as animal feed in times of drought. They also tried to start a cochineal dye industry with it.

  West of the Great Dividing Range, in the dry interior of New South Wales and Queensland, the cactus became a widespread weed. It turned 101,000 square miles of farming land into an impenetrable green jungle, in places 20 feet high. Farmers called it the green hell, and scores of them were driven off their land. Their abandoned homes were crushed under growth that advanced at a rate of 1 million acres per year.

  In 1919, the Australian federal government set up the Commonwealth Prickly Pear Board to coordinate eradication with the state governments. Mechanical removal and poisonous chemicals both failed. Biological control was a last resort. In 1925, the moth Cactoblastis cactorum was brought in from South America, and its larvae rapidly began to bring the infestation under control.

  Alan Dodd, son of the noted entomologist Frederick Parkhurst Dodd, was a leading official in the campaign. A memorial hall in Boonarga, Queensland, commemorates the moth's work. The release of cochineal insects has also proved effective in holding back the spread, because they eat the cactus and kill the plant at the same time.

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• 6. Table and Medicine

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  Raw opuntia leaves are 88% water and 10% carbohydrates, with less than 1% each of protein and fat. A 100 gram portion provides 41 calories, 16% of the Daily Value for vitamin C and 20% for magnesium.

  The fruit goes by many names, including cactus fruit, cactus fig, Indian fig and tuna. Indian here means Native American, not from India. It is edible but must be peeled with care, because glochids left on the skin lodge in the throat, lips and tongue. The Tequesta, a Native American people, rolled the fruit in grit to sand the glochids off. Others turned it in the flame of a campfire or torch. Seedless cultivars are available today, and the seeds can be turned into flour.

  In Mexico, prickly pear appears in appetizers, soups, salads, entrees, breads, desserts, candy, jelly and drinks, and the fruit is used for aguas frescas. The young stem segments, called nopales, go into dishes such as huevos con nopales and tacos de nopales. They are also an important ingredient in New Mexican cuisine, and they can be pickled. In 2009, nopales were introduced as a cheaper alternative to corn for making tortillas and other corn products. In the 1960s, a breeding program at the Antonio Narro Agrarian Autonomous University produced improvements in some traits, including cold-hardiness.

  Around the Mediterranean, almost every language has coined its own name. In Sicily, the fruit is called fichi d'India or ficurinia. In Sardinia it is figumorisca, meaning Moorish figs, and Catalan-speaking regions say figa de moro. In Andalusia, Spain, it is higos chumbos, and on Madeira it is tabaibo or figo tuno. Greeks call the figs frangosyka, meaning Frankish figs, or pavlosyka, meaning Paul's figs, depending on the region. In Albania it is fiq deti, or sea figs, and in Cyprus it is papoutsósyka or babutsa, meaning shoe figs.

  Malta calls the fruit bajtar tax-xewk, or spiny figs, and treats it as a typical summer fruit. The islanders also make a popular liqueur called bajtra. The plant is so common there that it often stands as a dividing wall between the terraced fields, in place of the usual rubble walls.

  Eritrea received the prickly pear during Italian colonisation, between 1890 and 1940. Locally it is called beles, and it is abundant from late July through September. The beles from the holy monastery of Debre Bizen is said to be particularly sweet and juicy. In Morocco, Tunisia, Libya, Saudi Arabia, Jordan and other parts of North Africa and the Middle East, yellow and orange varieties grow beside farms and railway tracks, on land that is otherwise noncultivable. Street vendors sell them in summer as a refreshing fruit.

  On St Helena, the cactus pear is called tungi. Colonial ivory traders brought the plants from East Africa in the 1850s, and they now grow wild in the dry coastal regions. Three principal cultivars grow there: the English, with yellow fruit, the Madeira, with large red fruit, and the small, firm spiny red. A local spirit also takes the name tungi. It is distilled from the opuntia cactus alone at the St Helena distillery at Alarm Forest, described as the most remote distillery in the world.

  In Mexican folk medicine, the pulp and juice are used for wounds and for inflammation of the digestive and urinary tracts. There is no high-quality evidence that opuntia helps with any of these. Before modern medicine, Native Americans and Mexicans mainly used it to close open wounds, splitting the stem or scraping out the pulp. The plants are edible, but the pointed hairs should not be eaten, and similar species with milky sap are suspect.

  The international research centre ICARDA is promoting and studying cactus pear, especially for India, Jordan and Pakistan. It is an underappreciated crop there and has recently expanded in cultivated area. In some particularly promising areas of India and Pakistan, it has given a 30% increase in milk yield per hectare.

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• 7. Cochineal and Beyond

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  Cochineal became Mexico's second-most valued export, behind only silver. Indigenous producers made it almost exclusively in Oaxaca. Buyers across Europe wanted the dyestuff so badly that its price was regularly quoted on the London and Amsterdam Commodity Exchanges.

  The source of this dye is Dactylopius coccus, a scale insect native to tropical and subtropical South America and Mexico. It is a mostly sessile parasite that lives on Opuntia cacti, feeding on the moisture and nutrients in the sap. The insect produces carminic acid, which deters predation by other insects. Extracted from the insect's body and eggs, the acid yields the red dye.

  The Aztec and Maya peoples of Central and North America used cochineal, and so did the Inca in South America. Today it serves mainly as a red food colouring and in cosmetics. Peru, the Canary Islands and Chile are the biggest producers. Current health concerns over artificial food additives have renewed its popularity, and rising demand makes insect farming attractive in other regions. Mexico is one of them, where production had declined again because the scale insect has numerous natural enemies.

  The cactus gives dye on its own account, too. The red dye betanin can be extracted from some Opuntia plants. The Navajo people have traditionally made a reddish dye from the fruit to colour woolen yarns.

  In arid and dryland regions, farmers use cactus as a fodder crop. Some prepare it by fermentation, which removes the spines and makes it easier for animals to digest. The thick skin of the nopal cactus can be harvested as an environmentally friendly replacement for leather. Bioethanol, a fuel, can also be produced from some Opuntia species.

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• 8. Emblem of Place

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  The coat of arms of Mexico shows a Mexican golden eagle perched upon an Opuntia cactus, holding a rattlesnake. The official history traces it to an Aztec legend about the founding of Tenochtitlan. The Aztecs, then a nomadic tribe, wandered in search of a sign. Their god Huitzilopochtli had commanded them to find an eagle devouring a snake, perched atop a cactus that grew from a rock submerged in a lake. After 200 years of wandering, they found the promised sign on a small island in the swampy Lake Texcoco and founded their capital there. The cactus, O. ficus-indica, called tenochtli in Nahuatl and full of fruits, is the symbol of that island.

  Malta's emblem, in its version from 1975 to 1988, included a prickly pear alongside a traditional dgħajsa, a shovel and pitchfork, and the rising sun. By legislation of 1995, the prickly pear is the official plant of Texas. For centuries the cactus has served as a food source and as a natural fence that keeps in livestock and marks the boundaries of family lands. It is resilient and often grows back after removal.

  Music has taken up the plant too. The British jazz and classical group Portico Quartet named a song after it. The Steely Dan song "My Rival", on the album Gaucho, opens with the words "The wind was driving in my face / The smell of prickly pear." The Uruguayan-born footballer Bruno Fornaroli is nicknamed prickly pear because of his sometimes spiky hairstyles.

  In the fall of 1961, Cuba had its troops plant an 8 mile barrier of Opuntia along the northeastern section of the 28 km fence around the Guantanamo Bay Naval Base. The aim was to stop Cubans from escaping to take refuge in the United States. It was dubbed the Cactus Curtain, a nod to Europe's Iron Curtain and the Bamboo Curtain in East Asia.

  The Hebrew word for the cactus fig is tzabar, and it is the origin of sabra, the term for any Jew born in Israel. The allusion is to a thorny, spiky skin on the outside and a soft, sweet interior. Sabras are said to be rough on the outside but sweet and sensitive once you know them. The word derives from the Arabic ṣubbār, and the related Arabic term sabr translates to patience or tenacity. According to a modern study, the prickly pear probably reached the Levant only around the 18th century.

  The prickly pear is also a national symbol of Palestine, where it has been grown across historic Palestine for centuries, traditionally to mark out land boundaries. Palestinians see it as representing resilience and patience, as in the proverb saber as-sabbar, which means the patience of the cactus. Its use as an emblem has been traced to a painting by the artist Zulfa al-Sa'di in the 1930s. Historical research on the Nakba in the 1980s and 1990s renewed its visibility, because it revealed that many destroyed Palestinian villages later saw cacti grow back. The plant's ability to thrive anywhere is also taken to reflect the experiences of the Palestinian diaspora.

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