Overview

Brief Summary

Biology

The six species of Opuntia found in the Galapagos are one of the principal sources of food for animals occupying areas of lowland. Tortoises and land iguanas eat the pads; doves, mockingbirds and iguanas eat the fruit; and finches eat the flowers, fruits and seeds, and obtain water from the succulent pads (8). Indeed Darwin was one of the first to notice the predilection of cactus finches for the fruits and flowers of Opuntia galapageia in particular (5). The animals that feed upon the fruit of Opuntias provide an indispensable service in dispersing the seeds stored within the nutritious flesh (8).
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Description

During his explorations of the Galapagos Islands, Darwin recorded Opuntia galapageia in a simple sketch of a tree-like cactus with a compact crown of pads (4) (5). While most Opuntia galapageia do indeed have well-developed trunks and rounded crowns (6) (7), some are more low-growing and shrubby in appearance (2). The flat, fleshy green pads are usually egg-shaped and dotted with evenly spaced clusters of 5 to 35 yellow to brown spines that are an obvious deterrent to predators (2) (6) (8). The trunk, when present, is initially covered with spines, but with age, develops dark reddish 'bark' (2) (6). Yellow flowers arise amongst the spine clusters and eventually develop into the spiny, spherical to oblong fruit, for which the genus gets the name 'prickly pear' (6).
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Biology

Interestingly, Opuntia helleri relies on birds to aid pollination, as the northern islands occupied by this cactus are not inhabited by any suitable insect pollinators (7). A number of bird species visit Opuntia helleri, including doves, cactus finches and mockingbirds. The soft-spines allow easy access to this species' flowers, and while feeding on the pollen, nectar and even petals, the birds receive a dusting of pollen which is transferred to, and fertilises, the other flowers visited (4) (7). This adaptation to bird pollination is only possible because the absence of large, herbivorous reptiles, such as giant tortoises, from the northern Galapagos Islands, allows Opuntia helleri to survive without the protection of hard, sharp spines (8) (9). Despite producing flowers all year round, Opuntia helleri's main flowering season occurs between November and February (9). Interestingly, even if the flowers are not pollinated, fruits and seeds may still develop. This is due to a remarkable process called apomixis, in which the female, unfertilised gametes develop into an embryo without needing to fuse with male gametes (10). Whether pollination occurs or not, fruits take several months to mature. Eventually dropping off the pads, many of the fruits are consumed by mockingbirds and cactus finches, which later pass the seeds in their faeces, thereby helping Opuntia helleri to disperse its offspring (7). Flowering only occurs in larger specimens of Opuntia helleri (8), but individuals of any size can reproduce simply by dropping their pads. In a process called vegetative reproduction, an entirely new plant may grow from the detached portion, giving rise to large thickets of cacti, all of which are genetically identical (7).
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Description

Forming large, sprawling thickets, Opuntia helleri is one of the characteristic cactus species of the northern Galapagos Islands (3) (4). The stem is divided into broad, fleshy pads up to 37 centimetres long and 22 centimetres wide, covered with evenly-spaced clusters of 7 to 28 yellowish-white or brown spines (4). In contrast with the strong, hard spines of many cactus species, the spines of Opuntia helleri are soft and flexible (4) (5). The pads produce striking yellow flowers, up to eight centimetres wide, from which large, green, fleshy fruits develop. Commonly known as “prickly pears”, these fruits are generally ovoid, covered in clusters of small spines and usually contain multiple seeds. Although generally a low-growing species, older specimens of Opuntia helleri will sometimes grow into a taller shrub or tree-like form up to two metres in height, developing a woody trunk with a coating of reddish-brown bark (4).
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Biology

The six species of Opuntia found in the Galapagos are one of the principal sources of food for animals occupying areas of lowland. Tortoises and land iguanas eat the pads; doves, mockingbirds and iguanas eat the fruit; and finches eat the flowers, fruits and seeds, and obtain water from the succulent pads (8). Indeed Darwin was one of the first to notice the predilection of cactus finches for the fruits and flowers of Opuntia galapageia in particular (5). The animals that feed upon the fruit of Opuntias provide an indispensable service in dispersing the seeds stored within the nutritious flesh (8).
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Description

During his explorations of the Galapagos Islands, Darwin recorded Opuntia galapageia in a simple sketch of a tree-like cactus with a compact crown of pads (4) (5). While most Opuntia galapageia do indeed have well-developed trunks and rounded crowns (6) (7), some are more low-growing and shrubby in appearance (2). The flat, fleshy green pads are usually egg-shaped and dotted with evenly spaced clusters of 5 to 35 yellow to brown spines that are an obvious deterrent to predators (2) (6) (8). The trunk, when present, is initially covered with spines, but with age, develops dark reddish 'bark' (2) (6). Yellow flowers arise amongst the spine clusters and eventually develop into the spiny, spherical to oblong fruit, for which the genus gets the name 'prickly pear' (6).
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Distribution

Endemic range

Opuntia galapageia is endemic to the Galapagos Islands of Ecuador in western South America; in fact, the three subspecies of this taxon are all endemic to the Galapagos Islands. This species is the furthest west occurring of all the cactaceae family species in South America.

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Range

Endemic to the Galapagos, the three subspecies all occur on different islands. Opuntia galapageia galapageia is found on Bartolomé, Santiago and Pinta Islands (7), O. g. macrocarpa is found on Pinzón Island, and O. g. profusa is foundon Rábida Island (6).
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Range

Endemic to the Galapagos, Opuntia helleri is restricted to the northern islands of Darwin, Genovesa, Marchena and Wolf (4).
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Range

Endemic to the Galapagos, the three subspecies all occur on different islands. Opuntia galapageia galapageia is found on Bartolomé, Santiago and Pinta Islands (7), O. g. macrocarpa is found on Pinzón Island, and O. g. profusa is foundon Rábida Island (6).
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Physical Description

Type Information

Type fragment for Opuntia myriacantha F.A.C. Weber
Catalog Number: US 3053103
Collection: Smithsonian Institution, National Museum of Natural History, Department of Botany
Verification Degree: Original publication and alleged type specimen examined
Preparation: Pressed specimen
Collector(s): R. Gosselin
Locality: Galápagos Is., Colón, Ecuador, Archipiélago de Colón, South America
  • Type fragment: Weber, A. A. 1898. Dict. Hort. 2: 894.
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Ecology

Habitat

Opuntia galapageia generally grows in the arid zone near sea level but is sometimes found in more forested areas at higher altitude (6) (7).
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Opuntia helleri is scattered throughout the arid lowlands, increasing in abundance towards the coast (4) (6).
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Opuntia galapageia generally grows in the arid zone near sea level but is sometimes found in more forested areas at higher altitude (6) (7).
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Molecular Biology and Genetics

Molecular Biology

Barcode data: Opuntia helleri

The following is a representative barcode sequence, the centroid of all available sequences for this species.


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Statistics of barcoding coverage: Opuntia helleri

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 1
Specimens with Barcodes: 1
Species With Barcodes: 1
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Conservation

Conservation Status

Status

Classified as Endangered (EN) on the IUCN Red List (1) and listed on Appendix II of CITES (3). Subspecies Opuntia galapageia galapageia is classified as Endangered (EN) on the IUCN Red List (1) and listed on Appendix II of CITES (3) and O. g. macrocarpa and O. g. profusa are classified as Vulnerable (VU) on the IUCN Red List (1) and listed on Appendix II of CITES (3).
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Status

Classified as Vulnerable (VU) on the IUCN Red List (1) and listed on Appendix II of CITES (2).
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Status

Classified as Endangered (EN) on the IUCN Red List (1) and listed on Appendix II of CITES (3). Subspecies Opuntia galapageia galapageia is classified as Endangered (EN) on the IUCN Red List (1) and listed on Appendix II of CITES (3) and O. g. macrocarpa and O. g. profusa are classified as Vulnerable (VU) on the IUCN Red List (1) and listed on Appendix II of CITES (3).
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Threats

In common with much of the native flora of the Galapagos, Opuntia populations have been negatively affected by agriculture, urbanisation, and the introduction of non-native animals and plants (8). Owing in particular to damage caused by feral animals such as goats and donkeys, Opuntia galapageia is now scarce in parts of its range where it was once abundant (4) (8) (9).
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The main threats affecting the Opuntia species found in the Galapagos are competition with invasive plants for space, light and nutrients; overgrazing by invasive herbivores such as goats and pigs; and expanding urban development and agriculture. Overgrazing is probably the most significant of these threats, since the consumption of dropped pads prevents vegetative reproduction, and means that only the larger plants capable of flowering are able to reproduce (8).
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In common with much of the native flora of the Galapagos, Opuntia populations have been negatively affected by agriculture, urbanisation, and the introduction of non-native animals and plants (8). Owing in particular to damage caused by feral animals such as goats and donkeys, Opuntia galapageia is now scarce in parts of its range where it was once abundant (4) (8) (9).
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Management

Conservation

With so many of the Galapagos's native animals dependant on Opuntias, the conservation of this cactus genus is critically important in the preservation of the archipelago's renowned biodiversity (10). The Charles Darwin Foundation is undertaking detailed surveys of Opuntia populations to establish appropriate conservation actions for each species. This is likely to involve the eradication of feral herbivores which has already been carried out successfully on several of the islands (8).
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Conservation

The Charles Darwin Foundation, a Galapagos conservation organisation, is working to restore damaged populations of Opuntia species. By conducting detailed surveys, they aim to determine the status and vulnerability of each species and develop specific conservation action plans to help preserve them (8).
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Conservation

With so many of the Galapagos's native animals dependant on Opuntias, the conservation of this cactus genus is critically important in the preservation of the archipelago's renowned biodiversity (10). The Charles Darwin Foundation is undertaking detailed surveys of Opuntia populations to establish appropriate conservation actions for each species. This is likely to involve the eradication of feral herbivores which has already been carried out successfully on several of the islands (8).
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Wikipedia

Opuntia saxicola

Opuntia saxicola is a species of plant in the Cactaceae family. This critically endangered species is endemic to the Galapagos Islands (Ecuador), where it is restricted to the island of Isabela.

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Opuntia helleri

Opuntia helleri is a species of plant in the Cactaceae family. This vulnerable species is endemic to the Galapagos Islands (Ecuador), where restricted to Wolf, Darwin, Marchena and Genovesa.

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Opuntia insularis

Opuntia insularis is a species of plant in the Cactaceae family. This endangered species is endemic to the Galapagos Islands (Ecuador), where restricted to Fernandina and Isabela.

References

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Opuntia galapageia

Opuntia galapageia is a species of plant in the Cactaceae family. It is endemic to the Galapagos Islands (Ecuador). There are three varieties: Opuntia galapageia var. galapageia on Bartolome, Santiago and Pinta, Opuntia galapageia var. macrocarpa on Pinzon and Opuntia galapageia var. profusa on Rabida.

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