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Asian frogbit (Hydrocharis dubia)

Asian frogbit is an introduced aquatic plant recorded as alien in Australia. Where it establishes, it can become invasive and may form dense growth that affects aquatic habitats and their use.

Key facts

Type: Weed, aquatic.

Native to: Southern and eastern Asia..

Established in: QLD, NSW.

Other names: Frogbit.

Best time to act: Inspect during the growing season when leaves are visible, and treat early before plants produce seed or spread vegetatively.

Identification

  • It is a perennial freshwater plant with floating or upright leaves.
  • Leaves are usually rounded, with a spongy, honeycomb-like surface and a single median stipule.
  • Primary leaf veins typically diverge from the midrib at an angle of about 50 to 85 degrees.
  • Roots usually extend into the bottom sediment rather than hanging free in the water.
  • It can reproduce by seed and by vegetative structures, including stolons, tubers and turions.
  • Look-alike: European frogbit (Hydrocharis morsus-ranae) is a close lookalike; it usually has two lateral stipules, flatter floating leaves and roots hanging freely in the water.

Where it grows

In Australia it grows in freshwater ponds, wetlands and water gardens, especially in still or slow-moving water.

Why it matters

  • It can become a noxious weed outside its natural range and may establish or spread in suitable northern Australian habitats.
  • Dense growth can shade native aquatic plants and alter habitat for other organisms.
  • Thick growth may obstruct water movement and interfere with access, recreation or waterway management.

How it spreads

  • It spreads by seed and vegetative propagules, including stolons, tubers and turions.
  • Waterfowl may carry seeds over long distances, while fragments can spread locally through water.
  • Boating, fishing equipment and other human activities can move plant material between waterbodies.

Control options

  • For small infestations, remove plants carefully and collect all fragments and vegetative material, since pieces left behind may spread or regrow.
  • Dispose of removed material securely away from water and do not dump it in drains, waterways or wetlands.
  • Where chemical treatment is appropriate, use only herbicides registered for aquatic weeds and approved for the site, following the label and local requirements.
  • Revisit treated sites regularly to check for regrowth and new plants, and report suspected infestations to the relevant state or territory biosecurity agency.

Hygiene and washdown

  • Before leaving an infested waterbody, remove plant fragments from boats, trailers, nets, fishing gear, footwear and machinery, and dispose of them securely on land.
  • Do not transfer untreated water, soil or plant material between waterbodies; clean and dry gear before reuse.
  • Inspect and clean vehicles, plant and footwear before leaving an infested area, paying attention to tyres, radiators, belly plates, tracks and floor mats.
  • Wash down at a designated bay where runoff is contained and can be monitored for seedlings.
  • Record each washdown so the client has evidence of clean entry and exit.

Classification by state

  • Australia (national): No national listing. Managed under state and territory law.
  • Queensland: Restricted matter, categories 3, 5. Do not give it away, sell or release it into the environment; do not keep it. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Not a priority weed. Not a state or regional priority weed in NSW. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • South Australia: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • Western Australia: Permitted, not declared. Listed as a permitted organism in WA, so it can be brought in, but it is not a declared pest.
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • Northern Territory: Check NT list. There is no NT weed profile for it. Check the NT declared weeds list for its current status.
  • Australian Capital Territory: Not declared. Not declared under the Biosecurity Act 2023 (ACT). A general biosecurity duty still applies.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

  • Queensland: Biosecurity Act 2014 (Qld), administered by Biosecurity Queensland (13 25 23)
  • New South Wales: Biosecurity Act 2015 (NSW), administered by NSW Department of Primary Industries and Regional Development

Sources