Prickly pear (Opuntia echios)

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Large specimen of prickly pear, Opuntia echios barringtonensis
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Prickly pear fact file

Prickly pear description

KingdomPlantae
PhylumTracheophyta
ClassMagnoliopsida
OrderCaryophyllales
FamilyCactaceae
GenusOpuntia (1)

The five varieties of Opuntia echios are quite variable in form, a phenomenon thought to result from adaptation to differing conditions on different islands (2) (3) (5) (6). The smallest, such as O. e. zacana, are shrubby and low-growing, never reaching more than a metre or two in height (2) (5) (7), while others, such as O. e. gigantea, grow into tall trees and are among the largest Opuntia species in the Galapagos (2) (3) (8). Opuntia echios usually has a well-developed trunk, which is spiny when young and later develops reddish, flaky bark (2) (3) (5). The more shrubby forms generally have softer spines, and tend to grow on islands where there are fewer browsing herbivores and lower competition with other plant species (3) (6) (9).

Opuntia echios produces flat, fleshy pads, up to 45 centimetres long and 32 centimetres wide, covered in evenly spaced groups of 2 to 20 or more yellowish to brown spines. The spines, up to 12 centimetres in length, tend to be erect, stiff and sharp on young plants, and more bristly, almost hairlike, on mature individuals (2) (5). The pads of Opuntia echios produce large yellow flowers, up to ten centimetres across, which develop into the greenish “prickly pear” fruits which give the Opuntia cacti their common name. These roundish to oblong fruits may be over seven centimetres in length, and are covered in spines and short, barbed hairs, known as glochids (2) (3) (5) (9).

Size
Height: up to 12 m (2) (3)
Trunk diameter: up to 1.25 m (2) (3)
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Prickly pear biology

Opuntia cacti are a key species in the ecology of the Galapagos Islands, the pads forming a major food source for tortoises and land iguanas, and the fruits being eaten by iguanas, doves and mockingbirds. The flowers, fruits and seeds are eaten by cactus finches, which may also obtain water by pecking at the fleshy pads (3) (9). In return, these species help to disperse the seeds of the cactus, and also act as important pollinators of the flowers, particularly on islands lacking insect pollinators such as bees (3) (9) (11). Flowering of Opuntia echios has been reported to occur between November and February, with each plant producing a few flowers every day throughout the flowering season. The seeds take several months to mature, and the long flowering season means that the fruits ripen over a period of time rather than simultaneously (11). The species may also be able to reproduce vegetatively (3), an entirely new individual growing from a detached portion of the plant. It is thought that the Opuntia species of the Galapagos Islands are very long-lived, potentially reaching ages of 150 years or more (8).

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Prickly pear range

Endemic to the Galapagos Islands, the five varieties of Opuntia echios occur on different islands. O. e. echios is found on Daphne Major, Santa Cruz, Baltra and Las Plazas Islands, O. e. barringtonensis is found on Santa Fé Island, and O. e. gigantea is found on Santa Cruz Island, in the vicinity of Academy Bay. O. e. inermis is known only from Volcán Sierra Negra, on Isabela Island, and O. e. zacana is found on Seymour Island, where it is the only Opuntia species on the island (2) (5) (7).

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Prickly pear habitat

Opuntia echios is commonly found in the arid zone, often growing in thin soil, sand or even bare lava, but also occurs at higher elevations in tropical dry forest (2) (7) (8) (10).

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Prickly pear status

Classified as Vulnerable (VU) on the IUCN Red List (1) and listed on Appendix II of CITES (4). Varieties Opuntia echios gigantea, O. e. inermis and O. e. echios are classified as Endangered (EN) and O. e. zacana and O. e. barringtonensis are classified as Vulnerable (VU) on the IUCN Red List (1).

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Prickly pear threats

In common with other Opuntia cacti on the Galapagos Islands, Opuntia echios is threatened by introduced plants, with which it competes for space, light and nutrients, and also introduced animals such as goats, donkeys, pigs and cattle. These non-native species often trample smaller Opuntia plants or eat into the trunks of older, less spiny individuals. If the cacti are knocked down and eaten, no vegetative reproduction can occur, and only the remaining larger plants are able to flower (9). The Galapagos Islands as a whole are also under increasing pressure from uncontrolled tourism, human population growth, farming and urbanisation (12) (13). The restricted ranges of many of the Opuntia echios varieties may make them particularly vulnerable to any threats.

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Prickly pear conservation

Opuntia echios receives some protection from international trade under its listing on Appendix II of the Convention on International Trade in Endangered Species (CITES) (4). However, the threats posed by introduced species and human activities need to be addressed if this cactus is to be adequately protected. The Charles Darwin Foundation is currently working in the Galapagos to research and survey all Opuntia populations, to help develop appropriate conservation actions for each species. These are likely to include the control of feral herbivores, as well as possible restoration projects (9)

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Find out more

To find out more about conservation in the Galapagos see:

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Authentication

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact: arkive@wildscreen.org.uk
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Glossary

Endemic
A species or taxonomic group that is only found in one particular country or geographic area.
Pollinator
An animal that in the act of visiting a plant’s flowers transfers pollen grains from the stamen (male part of a flower) to the stigma (female part of a flower) of a flowering plant. This usually leads to fertilisation, the development of seeds and, eventually, a new plant.
Variety
In taxonomy, the science of classifying organisms, variety is the rank below subspecies. Members of a variety differ from others of the same species in relatively minor ways.
Vegetative reproduction
Type of asexual reproduction (reproduction without recombination of genetic material) that results in the propagation of plants using only the vegetative tissues such as leaves or stems. The resulting plant is genetically identical to the original plant. A well-known example of this is the reproduction of strawberry plants from ‘runners’.
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References

  1. IUCN Red List (April, 2009)
    http://www.iucnredlist.org/
  2. Wiggins, I.L. and Porter, D.M. (1971) Flora of the Galápagos Islands. Stanford University Press, Palo Alto, California.
  3. Jackson, M.H. (1993) Galápagos: A Natural History. University of Calgary Press, Calgary.
  4. CITES (April, 2009)
    http://www.cites.org
  5. Anderson, E.F. (2001) The Cactus Family. Timber Press, Portland, Oregon.
  6. Racine, C.H. and Downhower, J.F. (1974) Vegetative and reproductive strategies of Opuntia (Cactaceae) in the Galapagos Islands. Biotropica, 6(3): 175 - 186.
  7. McMullen, C.K. (1999) Flowering Plants of the Galápagos. Cornell University Press, New York.
  8. Hamann, O. (2001) Demographic studies of three indigenous stand-forming plant taxa (Scalesia, Opuntia¸and Bursera) in the Galápagos Islands, Ecuador. Biodiversity and Conservation, 10: 223 - 250.
  9. Charles Darwin Foundation. (2006) Charles Darwin Research Station Fact Sheet: Opuntia cactus. Charles Darwin Foundation for the Galapagos Islands (AISBL), Galapagos, Ecuador. Available at:
    http://www.darwinfoundation.org/files/species/pdf/opuntia-en.pdf
  10. Hicks, D.J. and Mauchamp, A. (2000) Population structure and growth patterns of Opuntia echios var. gigantea along an elevational gradient in the Galápagos Islands. Biotropica, 32(2): 235 - 243.
  11. Grant, B.R. and Grant, P.R. (1981) Exploitation of Opuntia cactus by birds on the Galápagos. Oecologia, 49: 179 - 187.
  12. Oldfield, S. (1997) Cactus and Succulent Plants: Status Survey and Conservation Action Plan. IUCN/SSC Cactus and Succulent Specialist Group, IUCN, Gland, Switzerland and Cambridge, UK.
  13. UNEP-WCMC: Galápagos Islands National Park and Marine Reserve, Ecuador (May, 2009)
    http://www.unep-wcmc.org/sites/wh/pdf/Galapagos.pdf
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Image credit

Large specimen of prickly pear, Opuntia echios barringtonensis  
Large specimen of prickly pear, Opuntia echios barringtonensis

© Pete Oxford / naturepl.com

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