Botanical name: Chromolaena odorata    Family: Asteraceae (Sunflower family)
Synonyms: Eupatorium odoratum

Siam Weed is a big bushy herb or subshrub with long rambling (but not twining branches. In open areas it spreads into tangled, dense thickets up to 2 m tall, and higher when climbing up vegetation. Many paired branches grow off the main stem. The base of the plant becomes hard and woody while the branch tips are soft and green. The leaves are arrowhead-shaped, 5–12 cm long and 3–7 cm wide, with three characteristic veins in a ‘pitchfork’ pattern. They grow in opposite pairs along the stems and branches. As the species name ‘odorata’ suggests, the leaves emit a pungent odour when crushed. Clusters of 10–35 pale pink–mauve or white tubular flowers, 10 mm long, are found at the ends of branches. The seeds are dark coloured, 4–5 mm long, narrow and oblong, with a parachute of white hairs which turn brown as the seed dries. Siam weed is native to Tropical America, but is now naturalized throughout the tropics.
Medicinal uses: It is used as a traditional medicine in Indonesia. The young leaves are crushed, and the resulting liquid can be used to treat skin wounds.

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The flower labeled Siam Weed is ...