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Opuntia aurantiaca (Jointed cactus)

Life > eukaryotes > Archaeoplastida > Chloroplastida > Charophyta > Streptophytina > Plantae (land plants) > Tracheophyta (vascular plants) > Euphyllophyta > Lignophyta (woody plants) > Spermatophyta (seed plants) > Angiospermae (flowering plants) > Core Eudicots > Order: Caryophyllales > Familty: Cactaceae > Genus: Opuntia

Opuntia aurantiaca (Jointed cactus)

Opuntia aurantiaca (Jointed cactus), near Kirkwood in the Eastern Cape, South Africa. [photo H. Robertson, Iziko ]

Description

An inconspicuous plant that grows among the surrounding vegetation and is usually less than half a meter high although it can exceed this height by using adjacent scrub for support. Cladodes (the segments of stem modified for water storage and photosynthesis), are small and elongate and those that become rooted and buried become woody.  Woody cladodes and fruit constitute 7% of the cladodes in a stand of Jointed cactus plants and constitute 25% of the stand in terms of mass because these cladodes are relatively large (Robertson 1985a).

Jointed cactus plants have a number of different growth forms depending mainly on the amount of direct sunlight they receive. Three main growth forms can be distinguished:

  • explosed forms tend to be low growing and have small cladodes with long spines;

  • semi-shade forms have long spines, a high proportion of large cladodes and often exceed half a meter in height by using the surrounding bush for support; and

  • etiolated forms occur in the shade, also often exceeding half a meter in height, are characterised by elongate cladodes and in deep shade have short spines.

Distribution and habitat

A declared Category 1 invasive plant in South Africa.

Life cycle

  • The cladodes break off the plant easily and take root, often below the plant. This eventually results in the formation of stands of Jointed cactus plants, sometimes covering more than 5 m2 in ground area.
  • Other cladodes become attached to animals or are carried away by water and in this way are distributed over large areas.
  • The inedible fruits produced by Jointed cactus can also take root easily. The seeds they contain are 99.95% sterile (Archibald 1936) and so reproduction is almost entirely vegetative.

Ecological interactions

Herbivores in southern Africa

The following insects have been introduced to South Africa for biological control purposes and have become established:

  • Cactoblasis cactorum (Lepidoptera: Pyralidae: Phycitinae). This moth was introduced in 1933 for the biological control of Opuntia ficus-indica (Prickly pear) but it has a number of other cactus host plants, including Jointed cactus.  The orange and black striped larvae eat the parenchymous tissue inside the cladodes and cause moderate damage to Opuntia aurantiaca infestations (Klein 2011).

  • Dactylopius austrinus (Hemiptera: Dactylopiidae). A cladode sucker that was released in South Africa in 1935 for the biological control of Opuntia aurantiaca, and which causes extensive damage to this weed (Klein 2011). Dactylopius species are collectively known as cochineal insects and are all characterised by having vivid red body contents that from Dactylopius coccus is used for producing cochineal dye. The females suck the juices from the cactus and are easily noticed on the plant because of their untidy covering of waxy filaments, looking rather like blobs of cotton wool.

  • Mimorista pulchellalis (Lepidoptera: Crambidae: Spilomelinae). This moth was released in South Africa in 1979 for the biological control of Opuntia aurantiaca. Although it did initially become established, it is now regarded as not having become established (Klein 2011). Two other moth species: Nanaia sp. and Zophodia tapiacola (= Tucumania tapiacola) (both in the family Pyralidae) were also released but failed to become established.

Publications

  • Archibald E.E.A. 1939 The development of the ovule and seed of jointed cactus (Opuntia aurantiaca Lindley). South African Journal of Science 36. 195-211.
  • Klein H. 2011. A catalogue of the insects, mites and pathogens that have been used or rejected, or are under consideration, for the biological control of invasive alien plants in South Africa. African Entomology 19(2): 515-549.

    Moran V.C. and Cobby B.S.1979. On the life-history and fecundity of the cochineal insect, Dactylopius austrinus De Lotto (Homoptera: Dactylopiidae), a biological control agent for the cactus Opuntia aurantiaca. Bulletin of Entomological Research 69(4): 629-636. DOI: 10.1017/S0007485300020174 
  • Moran V.C.,  Zimmermann H.G. 1991. Biological control of jointed cactus, Opuntia aurantiaca (Cactaceae), in South Africa. Agriculture, Ecosystems & Environment 37(1-3): 5-27. doi:10.1016/0167-8809(91)90136-L

Text by Hamish Robertson


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