Water Weeds

Alligator Weed

Alternanthera philoxeroides

This plant is often confused with other species of Alternanthera (Joy weeds), Water Primrose (Ludwigia spp.), or Smartweeds, (Persicaria spp.) Difficult to identify in dense vegetation and when not in flower.
  • Family Amaranthaceae
  • Origin South America
  • Habit Perennial with mostly hairless surface stems that root at the nodes stoloniferous and underground stems producing shoots & roots (rhizomatous). Can form dense mats in or out of water.
  • Leaves Glossy green lance shaped leaves arranged in opposite pairs on hollow stems. Terrestrial plants can have reddish stems.
  • Flowers White, cylindrical to globe-shaped, papery, pom-pom like heads on stalks to 9cm long that arise from the leaf-stem junction. Summer.
  • Fruit Viable seed not recorded in Australia.
  • Roots Extensive underground rooting system to 1m deep.
  • Dispersal Vegetation spread by water, humans, animals (live stock), contaminated soil, earth moving machinery, boats and turf, Also spread by its misguided use as a culinary herb.
  • Control Mechanical and manual removal, foliar spray. Contact your local weed officer.
One of Australia’s worst aquatic weed threats. Adapted to growing on damp land, occasionally flooded land, in shallow water (rooted in the substrate), attached to the bank (in deep water) or free floating. Will survive for a few days in sea strength salinity and thrive in 10% sea strength (3,500 mg/I) saline water.

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