Widespread. Asia, Africa, North, South and Central America, Caribbean, Oceania. In many Pacific islands.
Invasive weed of plantations, pastures, grasslands, forests and forest margins, secondary fallows, sand dunes, waste areas, and roadsides. Threatens natural vegetation. Aggressiveness because large seed production (7000 from one plant). Produces chemicals inhibiting growth of competitors.
Perennial shrub, 1-1.5 m tall. Stems, greenish with purple, becoming round and woody. Leaves, oval, 5-8 cm long, opposite along stems, with saw-like margins. Flowers, dark blue, purple or violet, about 1 cm across, on spikes, up to 45 cm long, at top of stems, without stalks. Flowers, with five petals forming tube, with two stamens. Spikes become woody. Fruits develop within cavities. Seeds brown/black.
Spread: seeds, fur of animals; clothing; machinery; use as an ornamental;
Biosecurity: as an ornamental; contaminant of pasture seed; among 10 worst weeds in American Samoa, French Polynesia, Solomon Islands.