Biosecurity Spotters logo

Hydrocotyl (Hydrocotyle ranunculoides)

Hydrocotyl is an introduced aquatic weed that can form dense mats on still or slow-moving fresh water. It is a biosecurity concern in Australia, with infestations near Perth and a risk of harm to waterways if it spreads.

Key facts

Type: Weed, aquatic.

Native to: The Americas, tropical Africa and Asia.

Established in: NSW, WA.

Other names: Water pennywort, Floating pennywort, Floating marsh pennywort.

Best time to act: Inspect waterways during the active growing season, especially from spring to autumn when flowers are mostly present, and report suspected plants immediately.

Identification

  • A perennial plant that floats on water or grows along muddy banks and shallow margins.
  • Its green, hairless leaves are circular to kidney-shaped, up to 18 cm wide, and have 3–11 toothed lobes.
  • Leaf stalks attach to the underside of the leaf near its deepest lobe and can grow up to 40 cm long.
  • Long creeping stolons form tangled mats, with roots growing from nodes along the stems.
  • Small greenish, yellowish or white flowers grow in umbrella-shaped clusters below the leaves, mostly from spring to autumn.
  • Look-alike: Largeleaf pennywort (Hydrocotyle bonariensis) has leaves up to 12 cm wide, with shallow lobes and a stalk attached near the centre of the leaf.
  • Look-alike: Shield pennywort (Hydrocotyle verticillata) has much smaller leaves, about 2–4 cm across.

Where it grows

It grows in still or slow-moving fresh water, including rivers, wetlands, lakes and dams, and on the edges of still water bodies; infestations are reported near Perth, while it does not currently grow in NSW.

Why it matters

  • Dense mats can reduce water quality and outcompete native vegetation.
  • They can reduce habitat for fish and other animals.
  • Mats can restrict fishing, boating and swimming and reduce the visual appeal of waterways.

How it spreads

  • Water spreads the seeds, of which usually only one of the two in each fruit is viable.
  • Small stem fragments can regrow if they contain a node and may be moved by flowing water, waterbirds or human activities such as boating.

Control options

  • Do not attempt to treat or dispose of a suspected infestation yourself; report it promptly to the relevant state or territory biosecurity agency.
  • In NSW, report sightings to the NSW Biosecurity Helpline on 1800 680 244; NSW DPIRD leads the initial response.
  • Any physical removal should be directed or approved by biosecurity authorities and carefully contained, because fragments with nodes can regrow and spread.
  • Use herbicides only when advised and in accordance with aquatic-use registration, the product label and any applicable permit.

Hygiene and washdown

  • After working or boating in affected water, check boats, gear and equipment for plant fragments and clean them before moving to another waterway.
  • Do not move water or plant material from an infested site; follow biosecurity directions for any material removed.
  • 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: Not prohibited or restricted. Not listed as prohibited or restricted matter in Queensland. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Prohibited matter. It is an offence to deal with it, and you must notify NSW DPIRD as soon as you become aware of it.
  • Victoria: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • South Australia: Declared plant. Depending on the declaration, it can be an offence to move it on public roads or sell it, and landowners may be required to control it on their land.
  • Western Australia: Declared pest (C3). C3 Management: landholders must manage it to reduce its impact and stop it spreading.
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • Northern Territory: Not declared. Not on the NT A to Z weed list, and Weeds Australia does not list it as declared in the NT. Check the NT declared weeds list before moving or planting it.
  • 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.

  • New South Wales: Biosecurity Act 2015 (NSW), administered by NSW Department of Primary Industries and Regional Development
  • Western Australia: Biosecurity and Agriculture Management Act 2007 (WA), administered by the WA Department of Primary Industries and Regional Development

Sources