Siam Weed

Appearance

"Chromolaena odorata" is a rapidly growing perennial herb. It is a multi-stemmed shrub which grows up to 2.5 m tall in open areas. It has soft stems but the base of the shrub is woody. In shady areas it becomes etiolated and behaves as a creeper, growing on other vegetation. It can then become up to 10 m tall. The plant is hairy and glandular and the leaves give off a pungent, aromatic odour when crushed.

The leaves are opposite, triangular to elliptical with serrated edges. Leaves are 4–10 cm long by 1–5 cm wide. Leaf petioles are 1–4 cm long. The white to pale pink tubular flowers are in panicles of 10 to 35 flowers that form at the ends of branches. The seeds are achenes and are somewhat hairy. They are mostly spread by the wind, but can also cling to fur, clothes and machinery, enabling long distance dispersal. Seed production is about 80000 to 90000 per plant. Seeds need light to germinate. The plant can regenerate from the roots. In favorable conditions the plant can grow more than 3 cm per day.

Naming

Common names include Siam weed, Christmas bush, jack in the box, devil weed, Communist Pacha in Malayalam, common floss flower, rompe saragüey, Abani di egwu or Nsiibilibe, and triffid.

Defense

"Chromolaena odorata" contains carcinogenic pyrrolizidine alkaloids.
It is toxic to cattle.
It can also cause allergic reactions.
Recent research has shown the plant is larvicidal against all major mosquito vectors.

Uses

A recent review indicates that the ethno-pharmacological, fungicidal, nematicidal importance of the plant and its use as a fallow species and as a soil fertility improvement plant in the slash and burn rotation system of agriculture has contributed to its continued use and spread in Nigeria.