Opuntia
Opuntia, commonly called the prickly pear cactus, is a genus of flowering plants in the cactus family Cactaceae, many known for their flavorful fruit and showy flowers. Cacti are native to the Americas, and are well adapted to arid climates; however, they are still vulnerable to alterations in precipitation and temperature driven by climate change. The plant has been introduced to Australia, southern Europe, the Middle East, and parts of Africa.
Prickly pear alone is also used to refer to the fruit, but may also be used for the plant itself; in addition, other names given to the plant and its specific parts include tuna, sabra, sabbar, nopal, nostle from the Nahuatl word nōchtli, and paddle cactus. The genus is named for the Ancient Greek city of Opus. The fruit and leaves are edible. The most common culinary species is the "Barbary fig".
In places where they have been introduced outside their native range, some species in the genus Opuntia behave as aggressive invasive species.
Description
O. ficus-indica is a large, trunk-forming, segmented cactus that may grow to with a crown of over in diameter and a trunk diameter of. Cladodes are green to blue-green, bearing few spines up to or may be spineless. Prickly pears typically grow with flat, rounded cladodes containing large, smooth, fixed spines and small, hairlike prickles called glochids that readily adhere to skin or hair, then detach from the plant. The flowers are typically large, axillary, solitary, bisexual, and epigynous, with a perianth consisting of distinct, spirally arranged tepals and a hypanthium. The stamens are numerous and in spiral or whorled clusters, and the gynoecium has numerous inferior ovaries per carpel. Placentation is parietal, and the fruit is a berry with arillate seeds. Prickly pear species can vary greatly in habit; most are shrubs, but some, such as O. galapageia of the Galápagos, are trees.Growth
Taxonomy
When Carl Linnaeus published Species Plantarum in 1753 – the starting point for modern botanical nomenclature – he placed all the species of cactus known to him in one genus, Cactus. In 1754, the Scottish botanist Philip Miller divided them into several genera, including Opuntia. He distinguished the genus largely on the form of its flowers and fruits.Considerable variation of taxonomy occurs within Opuntia species, resulting in names being created for variants or subtypes within a species, and use of DNA sequencing to define and isolate various species.
Species
Opuntia hybridizes readily between species. This can make classification difficult, yielding a reticulate phylogeny where different species come together in hybridization. Opuntia also has a tendency for polyploidy. The ancestral diploid state was 2n=22, but many species are hexaploid or octaploid.Formerly in ''Opuntia''
- Austrocylindropuntia
- Brasiliopuntia
- Corynopuntia
- Cylindropuntia
- Disocactus phyllanthoides
- Micropuntia
- ''Miqueliopuntia''
Chollas
Breeding
One of the ancient homes of the cactus pear, Mexico, ran a breeding program in the 1960s. This effort at the Antonio Narro Agrarian Autonomous University produced improvements in some traits including cold-hardiness.Chemistry
Opuntia contains diverse phytochemicals in variable quantities, such as polyphenols, dietary minerals, and betalains. Identified compounds under basic research include gallic acid, vanillic acid and catechins, as examples. O. ficus-indica contains betalain, betanin, and indicaxanthin, with highest levels in their fruits.Distribution and habitat
Like most true cactus species, prickly pears are native only to the Americas. Through human action, they have since been introduced to many other areas of the world. Prickly pear species are found in abundance in Mexico, especially in the central and western regions, and in the Caribbean islands. In the United States, prickly pears are native to many areas of the arid, semi-arid, and drought-prone Western and South Central United States, including the lower elevations of the Rocky Mountains and southern Great Plains, where species such as O. phaeacantha and O. polyacantha have become dominant, and to the desert Southwest, where several types are endemic. Prickly pear cactus is also native to sandy coastal beach scrub environments of the East Coast from Florida to southern Connecticut, where O. humifusa, O. stricta, and O. pusilla, are found from the East Coast south into the Caribbean and the Bahamas. Additionally, the eastern prickly pear is native to the midwestern "sand prairies" near major river systems, such as the Mississippi, Illinois, and Ohio rivers. The plant also occurs naturally in hilly areas of southern Illinois, and sandy or rocky areas of northern Illinois.Opuntia species are the most cold-tolerant of the lowland cacti, extending into western and southern Canada. One subspecies, O. fragilis var. fragilis, has been found growing along the Beatton River in north-eastern British Columbia, southwest of Cecil Lake at 56° 17' N latitude and 120° 39' W longitude. Others are seen in the Kleskun Hills Natural Area of north-west Alberta at 55° 15' 30' N latitude and 118° 30' 36' W longitude.
Prickly pears produce a fruit known as tuna, commonly eaten in Mexico and in the Mediterranean region, which is also used to make aguas frescas. The fruit can be red, wine-red, green, or yellow-orange. In the Galápagos Islands, the Galápagos prickly pear, O. galapageia, has previously been treated as a number of different species, but is now only divided into varieties and subvarieties. Most of these are confined to one or a few islands, so they have been described as "an excellent example of adaptive radiation". On the whole, islands with tall, trunked varieties are also the home of giant tortoises, whereas islands lacking tortoises have low or prostrate forms of Opuntia. Prickly pears are a prime source of food for the common giant tortoises in the Galápagos Islands, so they are important in the food web.
Charles Darwin was the first to note that the cacti have thigmotactic anthers. When the anthers are touched, they curl over, depositing their pollen on the pollinator. That movement can be seen by gently poking the anthers of an open Opuntia flower. The same trait has evolved convergently in other genera.
Natural distribution of the plant occurs via consumption and associated seed dispersal by many animals, including antelopes, nonhuman primates, elephants, birds, and humans. When ingested by elephants, the sharp components of the plant cause harm to the mouth, stomach, and intestines.
Prickly pears were originally imported into Europe during the 16th century. They are now found in the Mediterranean region of Northern Africa, especially in Algeria, Morocco and Tunisia, where they grow all over the countryside, and in parts of Southern Europe, especially Spain, where they can be found in the east, south-east, and south of the country, and also in Malta, where they grow all over the islands, and in southern Italy, especially in Sicily and Sardinia. They can be found in enormous numbers in parts of South Africa, where they were introduced from South America.
The prickly pear is considered an invasive species in Australia, Ethiopia, South Africa, and Hawaii, among other locations.
Australia
The first introduction of prickly pears into Australia is ascribed to the founding governor of the New South Wales colony, Arthur Phillip, and the earliest European colonists, in 1788. Brought from Brazil to Sydney, they were most likely O. monacantha. That variety did not spread beyond the east coast. However, a number of other types of prickly pear were introduced to Australian gardens in the mid-19th century. The cactus was also used as agricultural fencing and a feedstock for animals in times of drought, as well as in an attempt to establish a cochineal dye industry.The cactus became a widespread invasive weed in the dry interior climate west of the Great Dividing Range, in New South Wales and Queensland, eventually converting of farming land into an impenetrable green jungle of prickly pears in places high. Scores of farmers were driven off their land by what they called the "green hell", and their abandoned homes were crushed under the cactus growth, which advanced at a rate of per year.
In 1919, the Australian federal government established the Commonwealth Prickly Pear Board to coordinate efforts with state governments to eradicate the weed. Early attempts, comprising mechanical removal and poisonous chemicals failed. As a last resort, biological control was attempted. In 1925, the Cactoblastis cactorum moth was introduced from South America, and its larvae rapidly began to control the infestation. Alan Dodd, the son of the noted entomologist Frederick Parkhurst Dodd, was a leading official in combating the prickly pear. A memorial hall in Boonarga, Queensland, commemorates the efforts of the moth. The release of cochineal insects, which eat the cactus and simultaneously kill the plant, has also proven an effective measure for combating its spread.