Source: "Weeds" - Auld and Medd Photo: Weeds CRC
Originating in South America, Alligator Weed is a terrestrial or aquatic (floating or rooted emergent) perennial herb found in slow moving and stationary waters forming large mats of interwoven roots and stems. As new stems are produced, old stems lose their leaves and become prostrate, thickening the underlying mat of this vigorous creeper.
Alligator Weed has a hollow purplish stem to 1cm wide. Leaves are opposite. Flowers are silvery white produced on a stalk to 9cm long that arises from the leaf-stem junction. Flowering from January to March. Fruit / seed produced but are rarely viable under Australian conditions. Viable seed not recorded in Australia. Reproduction is entirely vegetative
Spread by pieces in mud attached to machinery, and in turf where it may be inadvertantly spread by mowing. Breakup of stems and further spread is increased by herbicide use and the plant's reaction to the damage caused by the flea beetle, Agasicies hygophila.
Impact on bushland
Alligator Weed grows in fresh water, eventually covering the surface and destroying aquatic life. Can seriously impair water flow. It blocks rivers, streams and drains, worsening the effecs of flooding. The weed is grown in some gardens, being mistaken for a vegetable for use in asian dishes.
Alligator Weed is very difficult to control, with heavy infestations at Newcastle and around Sydney. Please contact your local control authority for advice on control.
Biocontrol: Biological control agents are effective in some coastal wetland situations on the aquatic plant form.
Alligator Weed is difficult to identify in dense vegetation. It may be confused with other Alternanthera species (eg. Alternanthera sessilis or Alternanthera denticulata - see the Look-a-likes booklet). These species have clustered flower heads in the leaf axils. Also Water Primrose species (Ludwigia spp) or Smartweeds (Persicaria spp).
WEEDeck, Sainty and Associates