Scientific name

Xanthium spinosumL.

Synonyms

Xanthium spinosum var. ambrosioides (Hook. & Arn.) Love & Dans.; Xanthium spinosum var. heterocephalum Widder; Xanthium spinosum var. inermeBel

Common names

Bathurst bur, spiny cocklebur, prickly burweed

Family

Asteraceae

Origin

Native to parts of South America

Naturalised distribution (global)

Xanthium spinosum is found in many countries between latitudes 50°N and 43°S. It is widely distributed in the Mediterranean region and Europe, throughout most of Australia, in some coastal African countries, and in southern parts of South America and the United States.

Introduced, naturalised or invasive in East Africa

Xanthium spinosum is considered to be potentially invasive in Kenya, Uganda and Tanzania. So far, no records of this species exist for East Africa, but it has been recorded in South Africa.

Habitat

A weed of pastures, croplands, waterways, grasslands, open woodlands, floodplains, waste areas, roadsides and disturbed sites in sub-tropical and sometimes also tropical, semi-arid, and arid environments and temperate areas.

Description

Xanthium spinosum is an upright (erect) and much-branched short-lived (annual) herbaceous plant usually growing 30-100 cm tall, but occasionally reaching up to 1.2 m in height, with spines at the base of the leaves.

The stems are greenish-yellow when young and are covered with fine hairs (finely pubescent). They are armed with spines that occur singly or in pairs at the base of each leaf stalk (in the leaf axils). These spines are usually three-pronged from near their bases and may appear to be several spines at first glance. They are yellow or greenish-white in colour with prongs 15-50 mm long.

The alternately arranged leaves (2-10 cm long and 6-30 mm wide) are borne on stalks (petioles) up to 30 mm long. The lower leaves are usually irregularly three-lobed, or occasionally with five lobes, with the middle lobe much larger than the others. However, on upper leaves the side lobes may be insignificant or absent, thereby giving the leaf blade an elongated (lanceolate) shape. The leaf upper surfaces are dark green and shiny with prominent whitish-coloured veins, while their undersides are pale green or whitish in colour with a dense covering of downy hairs.

Separate male and female (unisexual) flower-heads are produced on different parts of the same plant (this species is monoecious). Male flower-heads consist of numerous tiny flowers (i.e. florets) that are arranged in dense rounded clusters. These male flower-heads are borne at the tips of the stems, and are yellowish or creamy-white in colour. The greenish-coloured female flower-heads are borne singly or in small clusters in the upper leaf forks (i.e. axils), usually below the male flower-heads.

The fruit (8-15 mm long and 4-6 mm wide) is greenish when young, later becoming yellowish or straw-coloured, then eventually brownish as it matures. It is an oval-shaped (i.e. ellipsoid) 'burr' containing two seeds. These 'burrs' are stalkless (i.e. sessile), finely hairy, and covered in numerous small hooked spines (2-3 mm long). They also have two small, straight, spines or 'beaks' at the tip (1-2 mm long), which may be difficult to distinguish from the hooked spines. These fruit are mostly formed during late summer and autumn. The brown or black seeds (about 10 mm long) are flattened, and one of each pair is slightly larger than the other.

Reproduction and dispersal

This species reproduces entirely by seed, contained in the 'burrs'. These 'burrs' are well adapted for dispersal, due to their hooked spines, and readily become attached to animals, clothing and vehicles. The burrs may also be spread by water, in contaminated agricultural produce and they may also be spread by furry farm animals. The seeds can remain viable for several years.

Economic and other uses

Xanthium spinosum can be used as a medicinal plant but this cannot compensate for its overall negative impacts.

Environmental and other impacts

Xanthium spinosum invades pastures and grazing lands causing reductions in forage production. It is toxic to most domestic animals. It is also a serious agricultural weed.

Xanthium spinosum 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).

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.

All control efforts should be aimed at preventing seed formation. Single plants and small infestations can be hoed and larger infestations sprayed with herbicide. 

Young plants can be removed by hand for seedlings and saplings. It is difficult to remove larger plants by hand as they coppice readily. Various herbicides can be sprayed onto Xanthium spinosum for effective control. When using any herbicide always read the label first and follow all instructions and safety requirements. If in doubt consult an expert.

A range of biological control agents have been targeted at this species but with variable success (Bugwood wiki).

Legislation

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

References

BugwoodWiki online data sheet. Xanthium spinosum. http://wiki.bugwood.org/ Xanthium_spinosum#BIOLOGICAL_CONTROL. Accessed 13th March 2011.

Germplasm Resources Information Network (GRIN). www.ars-grin.gov/npgs/index.html. National Germplasm Resources Laboratory, National Genetic Resources Program, Agricultural Research Service (ARS), United States Department of Agriculture (USDA), Beltsville, Maryland, USA. Accessed March 2011.

Pacific Island Ecosystems at Risk (PIER). Xanthium spinosum L., Asteraceae: plant threats to Pacific ecosystems. www.hear.org/pier/species/ xanthium_spinosum. Institute of Pacific Islands Forestry, Hawaii, USA. Accessed March 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]