Asteraceae

Chromolaena odorata

Common Names: Siam weed

Plant Form: Upright thicket forming shrub Size: 1.5 to 3 m tall. Taller when climbing. Stem: Smooth, round, brittle, woody at base of trunk with age. Leaves: Soft, green, hairy, triangular, with 3 prominent veins. Flowers: Clusters of 10-35 pale pink or white tubular flowers with tassel-like protuberances. Fruit and Seeds: Brown to black 5 mm long with parachuting hairs and barbs. Habitat: Riverbanks, rainforest, waste areas, granite slopes, coastal areas. Distinguishing Features: May look like Billy goat weed (Ageratum conyzoides) while young, but develops more of a climbing or thicket habit with age. Impacts: Outcompetes and smothers crops and native vegetation through growth and allelopathy, increases fire risk, toxic to livestock, causes skin rashes and allergic reactions in humans.