Scientific name

Opuntia monocanthaHaw.

Synonyms

Opuntia vulgaris Mill.; Opuntia vulgaris auct. non P. Mill.

Common names

Drooping  prickly  pear, Barbary fig, cochineal prickly pear, common prickly pear, drooping pear, drooping tree pear, smooth tree pear, smooth-leaf tree pear, spiny prickly pear, spreading prickly pear.

Family

Cactaceae

Origin

South America (Brazil to northern Argentina)

Naturalised distribution (global)

Locations within which Opuntia monacantha is naturalised include  Australia, south-eastern USA, southern and eastern Africa, and some oceanic islands with warm climates.

Introduced, naturalised or invasive in East Africa

Opuntia monacantha is invasive in parts of Kenya, naturalised in parts of Tanzania and is present in Uganda (A.B.R. Witt pers. obs.).

Habitat

Moist savanna and coastal scrub also, agricultural areas, coastland, ruderal/disturbed sites.

Description

Opuntia monacantha is a succulent shrub or tree growing to 5m in height.

O. monacantha often has a definite trunk that is much branched at the top and has drooping upper branches (cladodes). Branches are narrowly obovate (egg-shaped in outline but with the narrower end at the base) to oblong-lanceolate; base somewhat tapered (cuneate), 10-35 cm long, 7.5-12.5 cm wide. Succulent branches bear areoles with 1-3 grey or yellowish to reddish brown spines with darker tips, while the trunk areoles have 10 or more spines.

Leaves are minute and are deciduous.

The stem segments (cladodes) are thin, flattened when young and longer (10-30 cm) than broader. They appear wilted, bright green and shiny when young.

The spines are 3-7 cm long, in groups of 1-2 or 3.

Flowers are 7.5-10 cm long, 5 -7.5 cm in diameter; outer perianth parts yellow with a reddish median stripe, 18-25 mm long, 12-15 mm wide. The inner perianth parts are yellow to orange, 25-40 mm long, 12-40 mm wide.

O. monacantha produces reddish-purple, fleshy, conical to obovoid  fruits that are about 60 mm long, prolific. The fruits are persistent on the plant.

Reproduction and dispersal

This species reproduces by stem fragments (cladodes may become dislodged and produce roots) and also by seeds.

Stem fragments may become attached to animals, footwear and vehicles. They are also dispersed by flood waters and in dumped garden waste. The fruit are eaten by various animals (e.g. birds and foxes) and the seeds then spread in their droppings.

Similar species

Opuntia monacantha is very similar to Opuntia stricta (common prickly pear) and Opuntia ficus-indica (sweet prickly pear). These species can be distinguished by the following differences:

• O. monacantha is a relatively tall shrub or tree-like plant (usually 2-5 m tall) with flattened and elongated (oblong or obovate) cladodes. These cladodes are hairless and have one or two large spines on most of the areoles on their surfaces. It has yellow flowers and reddish-purple fruit, and some of its cladodes droop towards the ground during fruiting.
• O. stricta is a low-growing plant (usually 50-100 cm tall) with relatively large flattened and elongated (elliptic or obovate) cladodes. These cladodes are hairless and generally do not have any spines (sometimes one or two large spines are present) on the areoles on their surfaces. The flowers are bright yellow and the fruit reddish-purple.
• O. ficus-indica is a relatively tall shrubby or tree-like plant (usually 1.5-3 m tall) with very large flattened and elongated (oblong, elliptic or obovate) cladodes. These cladodes are hairless and do not have any spines on the areoles on their surfaces. It has yellow flowers and reddish coloured fruit.

Economic and other uses

Opuntia monacantha is cultivated as an ornamental or as live hedge. It can be used as a medicinal plant, and the fruit is edible. However, these uses cannot compensate for this plant's overall negative impacts.

Environmental and other impacts

In Kenya as in South Africa Opuntia monacantha is considered to be a serious problem in some areas.  O. monacantha has been listed as a noxious weed in South Africa (prohibited plants that must be controlled. They serve no economic purpose and possess characteristics that are harmful to humans, animals or the environment) and most Australia states.

Management

The precise management measures adopted for any plant invasion will depend upon factors such as the terrain, the cost and availability of labour, the severity of the infestation and the presence of other invasive species. Some components of an integrated management approach are introduced below.

The best form of invasive species management is prevention. If prevention is no longer possible, it is best to treat the weed infestations when they are small to prevent them from establishing (early detection and rapid response). Controlling the weed before it seeds will reduce future problems. Control is generally best applied to the least infested areas before dense infestations are tackled. Consistent follow-up work is required for sustainable management.

Manual control can be effective when numbers of plants are very low but must be done carefully otherwise plant fragments will resprout into new plants, thus exacerbating the infestation. Both the spines make this a difficult and uncomfortable process). Burning of uprooted plants will help minimise this risk if there is enough dry material to ensure that the material burns. Plants can be treated by herbicide stem injections. When using any herbicide always read the label first and follow all instructions and safety requirements. If in doubt consult an expert.

Controlled burns have been used to control Opuntia species. Such burns must be well-timed and coordinated to reduce the risk of creating a bushfire and there must be sufficient material to carry a hot fire. Fire could be used for small, isolate stands but it will not penetrate large stands.

The moth Cactoblastis cactorum feeds on this plant in its larval stages and can help control Opuntia monacantha as part of an integrated control programme. It was introduced to Tanzania but never established. It is likely that some cochineal species which feed on Opuntia species have been introduced to East Africa. This group offers some prospects for biological control of Opuntia species.

Legislation

Not listed as a noxious weed by the state or governments in Kenya, Tanzania and Uganda.

Notes

The spines on the stem and glochids (barbed hairs or bristles) cause irritation on contact with the skin.

In some parts of the world, the spineless cultivars of Opuntia are exempt from restrictions associated with the more invasive spiny species.

References

Global Compendium of Weeds. www.hear.org/gcw. Hawaiian Ecosystems at Risk Project. Accessed March 2011. Accessed January 2011.

Henderson, L. (2001).  Alien weeds and invasive plants. A complete guide to declared weeds and invaders in South Africa.  Plant Protection Research Institute Handbook No. 12, 300pp. PPR, ARC South Africa.

Pacific Island Ecosystems at Risk (PIER). Opuntia Monacantha (Willd) Haw. Cactaceae: plant threats to Pacific ecosystems. www.hear.org/Pier/species/opuntia_monacantha.htm. Institute of Pacific Islands Forestry, Hawaii, USA. Accessed March 2011.

Wikipedia contributors. "Opuntia monacantha." Wikipedia, The Free Encyclopedia. Accessed January 2011.

Editors

Agnes Lusweti, National Museums of Kenya; Emily Wabuyele, National Museums of Kenya, Paul Ssegawa, Makerere University; John Mauremootoo, BioNET-INTERNATIONAL Secretariat - UK.

Acknowledgments

This fact sheet is adapted from The Environmental Weeds of Australia by Sheldon Navie and Steve Adkins, Centre for Biological Information Technology, University of Queensland. We recognise the support from the National Museums of Kenya, Tropical Pesticides Research Institute (TPRI) - Tanzania and Makerere University, Uganda. This activity was undertaken as part of the BioNET-EAFRINET UVIMA Project (Taxonomy for Development in East Africa).

Contact

BioNET-EAFRINET Regional Coordinator: [email protected]