Xanthium spinosum aka Spiny Cocklebur

Xanthium spinosum is an annual plant in the daisy family, Asteraceae. People call it spiny cocklebur and Bathurst burr. Names also include clotbur, clotweed, and thorny clotbur. Kew lists Argentina as its native range. Plants For A Future lists more of South America. Its list includes Brazil, Bolivia, Ecuador, Peru, Chile, Paraguay, and Uruguay. It does not say where the plant is native. Nor does it say where people brought it in. It also grows on disturbed ground in North America. It is not native to Britain or Ireland.

This plant grows about 1.6 feet [0.5 metres] tall. As an annual, it grows from seed each year. It blooms from July through October. Seeds ripen from August through October, while flowers still bloom. Each plant has both male and female flowers. Each flower is either male or female, not both. Plants For A Future says insects pollinate the flowers. It also calls the plant self-fertile. This means one plant can set seed without another nearby.

Grow it in a site with full sun. Plants For A Future says it cannot grow in shade. It grows in sandy soil, loam, and heavy clay. Soil can be slightly acid, neutral, or slightly alkaline. Though it copes with these soils, moist soil suits it best. The same source says it is easy to grow. It lists USDA hardiness zones 6–9 for this plant. Kew places it mostly in a subtropical climate. The sources give no detailed advice on frost protection.

Sow seeds in spring where you want the plants to grow. Plants For A Future says seeds need ample moisture to sprout. Plants can also spread by seed without help. Keep this in mind when choosing a garden bed. The source warns that this plant could become a weed. Disturbed ground also forms part of its known habitat. The evidence does not show how much it invades gardens.

Plants For A Future says this plant is poisonous. It also says the seeds hold toxins. The source lists no edible use; this is not a food plant. Past uses as a medicine include stopping bleeding and causing vomiting. These past uses do not prove it is safe or helpful. The source gives its use as medicine a low rating. It lists no other practical uses.