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Siam weed

Weed Habitat 

  • Native to Central and South America, Siam weed is a rapid invader of wet/dry tropical areas. It threatens native vegetation, pastures and many crops, and is toxic to stock.
  • Shade intolerant, produces chemicals that inhibit the growth of other plants.


  • An erect or sprawling, fast growing shrub.
  • Yellowish slender stems, sparsely hairy, much branched, lateral branches in pairs, forms a dense tangled bush and can scramble up to 20 m over trees.
  • Leavers are soft green, slightly hairy on both sides, roughly triangular and toothed on edges, 3 distinctive pitchfork veins, pungent smell when crushed.
  • Flowers are pale lilac, maturing to pink, tubular with protruding 2-branched stigmas, in terminal clusters.
  • Masses of small brown seeds, each with a tuft of hairs white at first and brown when dry.

Chromolaena odorataChromolaena odorataChromolaena odorata


Plant Type

Leaf Arrangement

Other weed identifiers

Plant Life Cycle

Weed Declaration

This species is declared Restricted Matter under the Biosecurity Act 2014 for further information on declaration refer to your Local Government or the Department of Agriculture and Fisheries.

Weed Spread