Xanthium L.

6 species naturalized Aust.; all states and territories

Monoeciouis, annual herbs. Leaves alternate. Heads in axillary clusters or short racemes. Male heads almost globular, surrounded by an involucre of free bracts in one row; corolla 5-toothed; stamens 5. Female head ovoid, 2-flowered, with an involucre in several rows; the lowest row remaining free; the upper consolidated into a hard burr, the free tips of the bracts becoming hooked spines; burr 2-beaked at the summit, 2-seeded; corolla absent. Cypselas ovoid, completely enclosed in the burr. Pappus absent.