Karroo thorn (Vachellia karroo)

PROHIBITED MATTER: If you see this plant report it to the NSW Invasive Plants & Animals Enquiry Line 1800 680 244
Also known as: Karoo acacia

Profile

Impact

Karroo thorn is an adaptable, vigorous shrub or tree that forms dense, thorny thickets and is well suited to Australia’s rangelands. It is fast growing, fire resistant and protected from browsing animals by its thorns. Karroo thorn is usually an evergreen tree, except during droughts or in very dry or cold localities, and grows to a height of 12 m.

Karroo thorn is identified as a threat to biodiversity. Dense thickets reduce agricultural productivity as they suppress the growth of grasses, prevent stock movement (including access to water) and add to the costs of mustering.

Distribution

It is present in southern Angola, Zambia, Zimbabwee and Mozambique and has been introduced into Libya, Morocco, Myanmar, India, Iraq, Corsica, Portugal, Sicily, Argentina, Bolivia, Chile, Paraguay, Spain and Mauritius. It is considered weedy in South Africa. Plant densities up to 2000 trees per hectare have been recorded in Eastern Cape Province.

As the favourite food of the black rhinoceros, it has been planted in botanic gardens and zoos in south eastern Australia to depict the African landscape. It was first recorded in Australia in Perth during the 1960s, possibly having spread from a residential planting or the Botanic Gardens. It was first recorded in NSW in Dubbo at Taronga Western Plains Zoo, but has since been eradicated. Currently there are no known infestations in NSW or Queensland.

Spread

The spread of karroo thorn seed occurs by wind, water and animal droppings. Intentional cultivation by humans has also occurred. Large trees can produce as many as 19 000 seeds per year. These seeds can remain viable in the soil for at least seven years. Seed germination is improved when the outer seed casing is disturbed through means such as fire, passing through the digestive tract of an animal, or gradual weathering over time.

Description

Karroo thorn has paired thorns (up to 10 cm long but can be 25 cm long) that protect the leaves from browsing animals. In some plants the bark is reddish-brown to dark brown or black and rough. Other plants may have bark that is pale greyish-white or greyish-brown and smooth.

Key identification features

  • Leaves (12 cm long; 5 cm wide) are light green and fern-like with small oblong leaflets in 8 to 20 pairs.
  • Flowers (1–1.5 cm diameter) are sweetly scented, fluffy, yellow and ball-shaped (similar to Australian wattle flowers). They grow in clusters of 4 to 6 balls.
  • Seed pods (16 cm long; 1 cm wide) are sickle-shaped, woody and slightly constricted between the seeds.
  • Seeds (3.5–9 mm long; 2–7 mm wide) are shiny brown and can remain attached to the pod by a thread-like membrane.

Habitat

Karroo thorn is the most widespread acacia in southern Africa, growing under many soil, climate and altitude conditions, only limited by intense cold or lack of moisture. Its preferred habitat and climate are similar climate to the native grasslands of central New South Wales (NSW) and southern Queensland, giving it the potential to become established over most of subtropical and southern Australia. It is also common in the coastal dune forests of Natal and watercourses of the Karroo region of central Cape Province, indicating further potential to threaten riparian areas in many parts of Australia.

Acknowledgements

Adapted by AnDi Communications from the CRC for Australian Weed Management Weed Management Guide: Karroo thorn. Reviewed by Rod Ensbey and Peter Gray.

References

CRC Weed Management Guide

Weed risk assessment – Karroo thorn, The State of Queensland, Department of Employment, Economic Development and Innovation, 2011

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Control

Your local council weeds officer will assist with identification, control information and removal of this weed. Infestations can be spread by inappropriate control activities. Early detection and eradication will prevent the spread of this weed.

Herbicide options

Contact your local council weeds officer for control advice for Karroo thorn (Vachellia karroo).

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Biosecurity duty

The content provided here is for information purposes only and is taken from the Biosecurity Act 2015 and its subordinate legislation, and the Regional Strategic Weed Management Plans (published by each Local Land Services region in NSW). It describes the state and regional priorities for weeds in New South Wales, Australia.

Area Duty
All of NSW General Biosecurity Duty
All plants are regulated with a general biosecurity duty to prevent, eliminate or minimise any biosecurity risk they may pose. Any person who deals with any plant, who knows (or ought to know) of any biosecurity risk, has a duty to ensure the risk is prevented, eliminated or minimised, so far as is reasonably practicable.
All of NSW Prohibited Matter
A person who deals with prohibited matter or a carrier of prohibited matter is guilty of an offence. A person who becomes aware of or suspects the presence of prohibited matter must immediately notify the Department of Primary Industries

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For technical advice and assistance with identification please contact your local council weeds officer.
For further information call the NSW Invasive Plants and Animals Enquiry Line on 1800 680 244 or send an email to weeds@dpi.nsw.gov.au

Reviewed 2017