Prickly pear  (Opuntia galapageia)

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).

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).

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 found on Rábida Island (6).

Opuntia galapageia generally grows in the arid zone near sea level but is sometimes found in more forested areas at higher altitude (6) (7).

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).

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).

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).

For further information on the conservation of endemic flora and fauna of the Galapagos see:

• The Charles Darwin Foundation:
  www.darwinfoundation.org