Alligator Weed

Alternanthera philoxeroides
Family: Amaranthaceae

Growth Habit: Alligator Weed can grow on damp soil or on water. In damp soil, underground stems can grow up to one metre in length. As an aquatic plant stems build up into large inter-woven mats.

Type of Plant: Alligator Weed is a perennial plant originating from South America.

Flowers: White paper-like, ball shaped flowers. The plant flowers in mid-summer. Flowers are located on short stems (2-7cm) and grow from the leaf stem joint.

Dispersal: Reproduces from nodes in Spring. The leaves and stems may die off but rhizomes and stems found underground can remain viable until favourable conditions return. As an aquatic weed it can break away and re-establish.

Distribution: Mostly found in Queensland and New South Wales waterways but poses a threat to most coastal areas, inland agricultural and urban areas where water is not limited.

Status: Alligator Weed is a Weed of National Significance and a declared species in Queensland.

Weed Impact: In water –

  • Restrict water flow in creeks, channels and drains
  • Impede access (recreation)
  • Damage pumping and irrigation equipment
  • Reduce water quality by preventing light penetration and reducing oxygenation of water
  • Create a favourable habitat for mosquitoes
  • Reduce water bird and fish activity
  • Make swimming dangerous
  • Cause death and reduction of fish and native plants
  • Costly and difficult to control
  • Competitive with species on land

Information referenced from “Queensland Government, Department of Natural Resources Pest Fact No PP4.”