Introduced, yearlong green, perennial, aromatic herb to 60 cm tall and covered in dense white hairs. Stems are erect, square in cross-section & much branched near the base. Leaves are oppositely arranged and crinkled. White zygomorphic flowers occur in clusters of 6-12 in the leaf axils; they form dry brown burrs with hooked spines. Germinates whenever there is sufficient rain; flowers throughout the year. A weed in a wide range of habitats where competition has been reduced by disturbance, overgrazing or previous grazing by sheep. Rarely invades undisturbed native vegetation and does not establish in cultivated paddocks. Prefers alkaline soils with low ground cover and rainfall of more than 200 mm. Seed spread by burrs attaching to animals and equipment, by water or in dung. Invasive, producing large numbers of long-lived seeds; causes vegetable fault in wool. Bitter tasting; unpalatable to stock; taints meat. Control options include hand-pulling, biological control agents, herbicides, burning, slashing, cultivation and sowing of competitive species.
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