Xanthium spinosum L.
Bathurst burr, spiny cocklebur, clotbur, spiny clotbur, prickly burrweed
South America, Chile
Erect, compact annual herb which may become woody and bushy to 1m. Much branched.
Able to survive in a wide range of climates and soil types, it therefore has a wide distribution. Prefers exposed, moderately warm situations in temperate regions on high fertility disturbed soils. It is widespread in Australia, preferring drier climates. Mainly a pasture weed, also a weed in summer growing crops. Often associated with sheep camps, watercourses, dam banks and floodplains.
Stems and Leaves:
The leaves are up to 7cm long divided into 3 irregular lobes, the central lobe narrowing to a longer point. The upper surface of the leaf is shiny dark green with short appressed hairs denser on the veins. The lower surface of the leaf is pale green and downy. The leaves are arranged alternately on the stem. The stems are erect and slightly curved with many branches. The stems have yellow/green 3 pronged spines at the base of each leaf or branch.
Flowers and Fruit:
Male flowers are in terminal spikes at the ends of branches or in the upper leaf axils. They are small green/white and inconspicious. Female flowers form lower on the stem at the leaf axils and at the nodes. The female flowers become the burrs which are the fruit containing the seeds. Burrs are egg shaped, 1cm long with hooked spines that are 3mm long and terminal spines are 1-2mm long. Flowers most of the year.
This plant is a declared noxious weed in NSW. It has rigid pronged green/yellow spines at the base of the leaves. There are small hairs along yellow veins of the top side of the shiny green up to 25mm long leaves . Xanthium spinosum can be distinguished from Xanthium cavanillesii in that the latter has stems without spines at the base of the leaves, the leaves are shallowly and unevenly lobed and the burrs are 15-30mm long. X. spinosum can also be distinguished from Xanthium occidentale (Noogoora burr, cockle burr) which has stems without spines at the base of the leaves; the leaves have definite lobes usually 3-5 lobes and burrs that are 16-18mm long.
Sources & References
Auld BA, Meld RW (1992) 'Weeds an illustrated botanical guide to the weeds of Australia.' (Inkata Press: Melbourne)
Harden GJ (Ed) (2002) 'Flora of New South Wales.' (University of New South Wales Press Ltd: Sydney, Australia)
Parsons WT, Cuthbertson EG (2001) 'Noxious weeds of Australia.' 2nd edn. (CSIRO publishing: Collingwood, Victoria)
Lloyd S (2000) 'What should you know about bathurst burr'
Queensland Government Natural Resources and Mines (2004)
State Noxious Weed Control Board of Western Australia (2003) www.nwcb.wa.gov
Prepared by Kylie Pethybridge, 2005
Checked by Carole Campbell, 2005
Updated by Justin KY Chu, July 2005
Checked by Dr Peter Michael, July 2005