Australian Tropical Rainforest Plants - Online edition

Chromolaena odorata (L.) R.M.King & H.Rob.

Shrub (woody or herbaceous, 1-6 m tall)
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Flowers and leaves. © S.G. McKenna
Flowers. © S.G. McKenna
Habit, leaves and flowers. © S.G. McKenna
Leaves. © A. Ford
Herbarium specimen. © CSIRO
Leaf showing three primary veins. © CSIRO
Herbarium specimen showing leaf underside and flowers. © CSIRO

King, R.M. & Robinson, H.E. (1970) Phytologia 20(3): 204. Type: .

Common name

Siam weed


Scrambling shrub to 7 m tall, often around 4 m tall. Stem round in cross-section.


Simple, entire or toothed, triangular, 4.5-12 x 20-55 mm; upperside hairy; underside densely hairy, dotted with glands visible with a hand lens. Petioles 10-17 mm long. Three conspicuous main veins running from near base to tip. Have a pungent odour when crushed. Young leaves may be partly purplish.


Inflorescence axillary or terminal panicles of heads. Flowers ca. 5 mm diameter, white, pink or purple; ray florets absent; bracts green, 2-9 mm long.


A nut, ca. 4-5 mm long, pappus of pale brown plumes.


Features not available.

Distribution and Ecology

An introduced species. Naturalised in NEQ and one record from CEQ in 2013, but subject to an eradication program. Altitudinal range from near sea level to 30 m. Found in and on the edges of rainforest and open forest and woodlands.

Natural History & Notes

A declared noxious weed. Considered to be one of the world's worst weeds.

Eupatorium odoratum L., Systema Naturae Edn. 10 2: 1205(1759).
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