Widespread. Africa, Asia, North, South and Central America, Caribbean, Europe, Oceania. In most Pacific islands.
Important, invasive, weed of plantations, upland rice, food crop gardens, pastures, roadsides, waste sites. Fast growing, smothering other species, flowering early and producing much seed with long survival. Cattle avoid it.
Stems, 4-sided with short, stiff, backward-pointing thorns. Leaves, alternate along stems, bright green, 10-20 cm long, divided into 4-9 pairs of leaf-like segments, each with 12-30 pairs of leaflets. Flowerheads, a cluster of pink to purple, individual flowers, with long stamens forming fluffy balls, on short prickly stalks. Seedpods, soft, spiny, in clusters, breaking into 2-4, 1-seeded parts.
Spread: seeds by birds, other animals, clothing, in flowing water; use as a ground cover; moved in road materials; as pasture seed contaminant.
Biosecurity: high risk of introduction. Among 10 worst weeds in Fiji, Samoa, Solomon Islands. In Australia, 'restricted invasive plant': do not release into environment, give away or sell.
Biocontrol: Heteropsylla spinulosa, psyllid, introduced into Australia, PNG, Samoa. Fungus, Corynespora cassiicola, has potential.
Cultural control: before flowering, hand weed (use gloves or hoe!) or slash; vehicle hygiene.
Chemical control: in Australia: dicamba; diuron; fluroxypyr; glufosinate-ammonium. In Fiji, glyphosate. Apply to regrowth after slashing or burning.