Siam weed

Chromolaena odorata (Siam weed), also called communist weed, is a perennial herb or scrambling shrub of the aster family (Asteraceae), genus Chromolaena, 1–2 m tall (clambering to 5–10 m in favourable conditions with its soft stems). The stems are branched and finely hairy. The **leaves are opposite, ovate-lanceolate, toothed and three-veined**, 4–10 cm long, and give off a characteristic pungent aroma when crushed. The **small pale lilac/pink flowers** are grouped into tiny flower heads (capitula) arranged in terminal corymbs; each head contains only tubular florets. The fruit is an achene (cypsela) bearing a pappus of hairs that aids wind dispersal.

Updated by lebachungtdh@gmail.com · 10/12/2026

Chromolaena odorata is native to tropical America (Mexico, the Caribbean, South America) and, after introduction, became a **serious invasive species** across the Old World tropics (Southeast Asia, Africa, Oceania), spreading fast on open ground, roadsides, swidden fields and plantations. Besides being a weed, its **leaves** are used in folk medicine (poultices for wounds, to stop bleeding, as an antiseptic) in many countries; the plant is also used as green manure and gives honey. **Note**: it is toxic to livestock and its pollen can cause allergies. It has not been assessed by the IUCN and is therefore listed as Not Evaluated (NE).

Updated by lebachungtdh@gmail.com · 10/12/2026