Prickly pears
Opuntia
Summary 9
Opuntia is a genus in the cactus family, Cactaceae.
Description 10
O. ficus-indica is a large, trunk-forming, segmented cactus that may grow to 5–7 m (16–23 ft) with a crown of possibly 3 m (10 ft) in diameter and a trunk diameter of 1 m (3 ft 3 in). Cladodes (large pads) are green to blue-green, bearing few spines up to 2.5 cm (1 in) or may be spineless. Prickly pears typically grow with flat, rounded cladodes (also called platyclades) 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 epiperigynous, 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 Opuntia echios of the Galápagos, are trees.
O. ficus-indica thrives in regions with mild winters having a prolonged dry spell followed by hot summers with occasional rain and relatively low humidity. A mean annual rainfall of 350–500 mm (14–19 1⁄2 in) provides good growth rates. O. ficus-indica proliferates in various soils ranging from subacid to subalkaline, with clay content not exceeding 15–20% and the soil well-drained. The shallow root system enables the plant to grow in shallow, loose soils, such as on mountain slopes. Opuntia spreads into large clonal colonies, which contribute to its being considered a noxious weed in some places.
Animals that eat Opuntia include the prickly pear island snail and Cyclura rock iguanas. The fruit are relished by many arid-land animals, chiefly birds, which thus help distribute the seeds. Opuntiapathogens include the sac fungusColletotrichum coccodes and Sammons' Opuntia virus. The antCrematogaster opuntiae and the spiderTheridion opuntia are named because of their association with prickly pear cactus.
Distribution 10
Like most true cactus species, prickly pears are native only to the Americas. Through human actions, 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 (West Indies). In the United States, prickly pears are native to many areas of the arid, semiarid, 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 Opuntia phaeacantha and Opuntia polyacantha 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 Opuntia humifusa, Opuntia stricta, and Opuntia 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" nearby 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 central British Columbia, southwest of Cecil Lake at 56° 17’ N latitude and 120° 39’ W longitude.
Prickly pears also produce a fruit, commonly eaten in Mexico and in the Mediterranean region, known as tuna; it also is used to make aguas frescas. The fruit can be red, wine-red, green, or yellow-orange. In the Galápagos Islands, six different species are found: O. echios, O. galapageia, O. helleri, O. insularis, O. saxicola, and O. megasperma. These species are divided into 14 different varieties; 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 have giant tortoises, and 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 these cacti have thigmotacticanthers; when the anthers are touched, they curl over, depositing their pollen. This movement can be seen by gently poking the anthers of an open Opuntiaflower. The same trait has evolved convergently in other species (e.g. Lophophora).
The first introduction of prickly pears into Australia is ascribed to Governor Phillip and the earliest colonists in 1788. Brought from Brazil to Sydney, prickly pear grew in Sydney, New South Wales, where they were rediscovered in a farmer's garden in 1839. They appear to have spread from New South Wales and caused great ecological damage in the eastern states. They are also found in the Mediterranean region of Northern Africa, especially in Morocco and Tunisia, where they grow all over the countryside, and in parts of Southern Europe, especially Spain, where they grow in the east, south-east, and south of the country, and also in Malta, where they grow all over the islands. They can be found in enormous numbers in parts of South Africa, where they were introduced from South America.
Prickly pears are considered an invasive species in Australia, Ethiopia, South Africa, and Hawaii, among other locations.
Prickly pears (mostly Opuntia stricta) were originally imported into Europe during the 1500s and Australia in the 18th century for gardens, and were later used as a natural agricultural fencing and in an attempt to establish a cochineal dye industry. In Australia, they quickly became a widespread invasive weed, eventually converting 260,000 km2 (101,000 sq mi) of farming land into an impenetrable green jungle of prickly pear, in places 6 m (20 ft) high. Scores of farmers were driven off their land by what they called the "green hell"; their abandoned homes were crushed under the cactus growth, which advanced at a rate of 4,000 km2 (1,000,000 acres) 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 at mechanical removal and poisonous chemicals failed, so in a last resort, biological control was attempted. The mothCactoblastis cactorum, from South America, whose larvae eat prickly pear, was introduced in 1925 and rapidly reduced the cactus population. The son of the noted entomologist Frederick Parkhurst Dodd, Alan Dodd, was a leading official in combating the prickly pear menace. A memorial hall in Chinchilla, Queensland, commemorates the moth.
Natural distribution occurs via consumption and seed dispersal by many animals, including antelopes, nonhuman primates, elephants, birds, and humans.
Growth 10
Bud appears ►
Bud grows ►
Bud begins pad transformation ►
Bud completes pad transformation ►
Pad continues growth ►
Edible pad (tender) ►
Mature pad
Sources and Credits
- (c) José Belem Hernández Díaz, some rights reserved (CC BY), uploaded by José Belem Hernández Díaz
- (c) sergio niebla, some rights reserved (CC BY-SA), https://www.flickr.com/photos/22048801@N03/17389900852/
- (c) sergio niebla, some rights reserved (CC BY-SA), https://www.flickr.com/photos/22048801@N03/17389718835/
- (c) Megan Hansen, some rights reserved (CC BY-SA), https://www.flickr.com/photos/nestmaker/5575777484/
- (c) Peter Stenzel, some rights reserved (CC BY-ND), https://www.flickr.com/photos/peterstenzel/37638164515/
- (c) CameliaTWU, some rights reserved (CC BY-NC-ND), https://www.flickr.com/photos/cameliatwu/10355346796/
- (c) Amante Darmanin, some rights reserved (CC BY), https://www.flickr.com/photos/amantedar/5661406844/
- (c) Antonio Moreno Talamantes, some rights reserved (CC BY-NC), uploaded by Antonio Moreno Talamantes
- Adapted by Jeny Davis from a work by (c) Wikipedia, some rights reserved (CC BY-SA), https://en.wikipedia.org/wiki/Opuntia
- (c) Wikipedia, some rights reserved (CC BY-SA), https://en.wikipedia.org/wiki/Opuntia
