Amazon frogbit

A native to Central and South America, Amazon frogbit is a perennial fast-growing, floating, aquatic plant, reminiscent of a large duckweed (Lemna minor). Leaves generally float on the water surface but can become emergent when the plant is crowded.

It can often be found in fishponds, aquariums and water features. This invasive aquatic plant invades and smothers waterways. It can form large dense mats of runners and adult plants can develop very quickly. It can also block waterways and irrigation channels limiting recreational activities.

Amazon frogbit is not a prohibited or restricted invasive plant under the Biosecurity Act 2014.

Scientific name

Limnobium laevigatum

Description

  • Perennial floating aquatic plant that can grow up to 50cm high.
  • Leaves are bright green, up to 4cm wide, are either floating or emergent and arranged in basal rosettes along runners (stolons).
  • Flowers are white to pale yellow, male or female, up to 13mm wide.
  • Flowers emerge upright, and subsequent fruit develop on the underside of the plant, in the water. Both fruit and flowers are hard to see.
  • Fruit is about 4–13mm long, 2–5mm wide and contains up to 100 highly viable seeds, which are less than 1mm diameter and spherical with a rough surface.
  • Fruit are retained on the plant but split when mature, releasing seeds which mostly sink.

Habitat

  • Prefers tropical to subtropical climates. It may become naturalised in dams, lakes and freshwater wetlands throughout Queensland.

Distribution

  • First occurrence in the Queensland environment was detected in March 2011 with establishment of the plant in a Redlands waterway adjoining an urban area.
  • As this plant has been sold as an aquarium plant for some time, it may be likely that encounters in waterways near urban areas throughout Queensland are a result of escapes or releases from aquariums or from garden water features.
  • It has also been detected in Gold Coast and Sunshine Coast waterways and a major infestation has occurred in the Barron River catchment in North Queensland.
  • Also found in rivers and creeks.

Life cycle

  • Seed banks can exist in soil for at least 3 years.
  • Grows from seed and through vegetative reproduction, with vegetative reproduction the most important method of propagation.

Impacts

Environmental

  • Forms dense mats that smother native aquatic plants.
  • Reduces oxygenation of water.

Economic

  • Large infestations interfere with watercraft.
  • Degrades quality of swimming and fishing.
  • Interferes with water treatment plant/water management/hydroelectricity infrastructure, e.g. Barron River.

How it is spread

  • Spreads by seeds and stem fragments. Floating rosettes produce runners (stolons), the ends of which grow into juvenile plants.
  • It can also be spread by careless dumping of unwanted plants into urban drains leading into waterways. Young plants can easily and quickly be carried along by water.

Control

  • The best approach is to combine herbicide and physical control methods. The control methods should suit the specific plant and particular situation.

Physical control

  • Plants in ponds or small dams can be removed by physical and mechanical means, taking care to remove all root mass. Follow-up will be required.

Herbicide control

  • The Australian Pesticide and Veterinary Medicines Authority (APVMA) has recently registered a herbicide for the control of Amazon frogbit in Queensland.
  • Read the Amazon frogbit fact sheet (PDF, 3.8MB) for herbicide control and application rates.

Legal requirements

  • This is not a declared species under the Land Protection (Pest and State Route Management) Act 2002 but may be declared under other legislation or local government law.

Further information