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Plant 395


Opuntia species (Cactaceae)

Prickly pear





Opuntia is the largest genus in the cactus family with 129 accepted species currently recognised. Opuntia species are most well known for their flat stem sections, which are called cladodes, but commonly referred to as pads. However, some species have cylindrical stems and globular cladodes. Plant size, flower colour and spine structure and arrangement vary greatly among species.

Opuntia, in subfamily Opuntioideae, have unique spines called glochids. These may appear soft and fuzzy to the human eye, but these small, often barbed spines detach easily from the plant and cause great irritation when lodged in the skin – moreover, they are very difficult to remove. Species may only have glochids or may have them in addition to larger spines.

The common name prickly pear reflects the shape of the edible fruit, which historically has been used as a food source. Other historical uses include: a natural fence to maintain boundaries and corral livestock; a fodder crop, particularly in arid areas; and to farm the scale insect Dactylopius coccus. Dactylopius is the source of cochineal, a dye used for food colouring and in cosmetics.

Opuntia species are native to the Americas but have been introduced to many countries that have suitable sub-tropical or Mediterranean climates. In many of these introduced countries, prickly pears have become invasive due to their ability to propagate themselves from fallen pads, with plants forming large, clonal clumps. The lack of natural pest control also contributes to their spread.

Opuntia species introduced to Australia in the eighteenth century quickly became formed widespread, impenetrable populations that forced farmers from the land. By 1920, infestations covered 58 million acres (c. 23 million hectares) and were estimated to advance by 2.4 million acres (c. 970,000 hectares) per year. When eradication by mechanical and chemical means failed, they became an early subject for biological control with the introduction of the cactus moth Cactoblastis cactorum and Dactylopius coccus from the species’ native ranges. By 1932, nearly 17 million acres (c. 6.8 million hectares) of land had been returned to agricultural use.

Recently, other uses have been found for prickly pears. A plant-based leather has been developed in Mexico, which uses less water than traditional leather manufacture and few chemicals to produce it, with no greenhouse gas emissions. Moreover, Mexican researchers have produced biodegradable bioplastic from Opuntia species with research ongoing to determine which species will be best for use on an industrial scale.

Charles, G 2006. Cacti and succulents: an illustrated guide to the plants and their cultivation. The Crowood Press Ltd.

Department of Agriculture and Fisheries 2020. The prickly pear story. The State of Queensland, Australia.


Louisa Hall


The 25th July 2021 marks 400 years of botanical research and teaching by the University of Oxford.

As a celebration and count-down to this anniversary, the University of Oxford Botanic Garden and Arboretum, together with the Oxford University Herbaria and the Department of Plant Sciences, will highlight 400 plants of scientific and cultural significance. One plant will be profiled weekly, and illustrated with images from Oxford University's living and preserved collections.





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Contacts

Dr Stephen Harris (stephen.harris@plants.ox.ac.uk)