Xanthium cockle burrs are invasive weeds in many countries, affecting local ecosystems and agriculture. All Xanthium in Australia are naturalised weeds from multiple overseas sources, but their taxonomic identities are contentious. In particular, species identities of four burr varieties or “complexes” under Xanthium section Xanthium in Australia are unclear. These complexes, commonly referred to as “Noogoora”, “Californian”,...