Siam weed

Chromolaena odorata

In the open, Siam weed grows as a dense tangling bush to 2−3 m. However, it can scramble up trees to a height of 20 m. Several stems develop from the crown of the plant. The leaves of Siam weed are soft, green, hairy and triangular in shape, with a distinctive three-vein ‘pitchfork’ pattern. New growth exhibits a purple colouration. The stems are smooth, round and fairly brittle, becoming woody at the base when old.