Hydrocotyl (Hydrocotyle ranunculoides)

Also known as: water pennywort, floating pennywort

Hydrocotyl is a fast growing water weed with circular or kidney shaped leaves. It forms dense mats over still or slow-flowing freshwater including rivers, wetlands, lakes and dams.

Profile

How does this weed affect you?

Hydrocotyl forms dense mats that:

• reduce water quality
• outcompete native vegetation
• reduce habitat for fish and other animals
• can limit recreational activities such as fishing, boating and swimming
• reduce the visual appeal of waterways.

What does it look like?

Hydrocotyl is a perennial plant that can grow over water or on the edge of waterways. If on the edge or in shallow water, it has long stolons that creep in the mud. When floating, it forms a tangled mass of roots and leaf stems that can be submerged up to 50 cm into the water. In cold regions it is dormant over winter.

Leaves are:

• either floating or growing up to 40 cm above the water’s surface or muddy bank
• green
• up to 18 cm wide
• circular to kidney-shaped
• hairless
• lobed with 3–11 deep or shallow lobes with toothed edges
• on succulent stalks 2–40 cm long, which are attached on the underside of the leaf near the deepest lobe
• alternate along the stems.

Flowers are:

• greenish, yellowish or white with five petals
• 2–3 mm in diameter
• below the leaf canopy
• in umbrella shaped clusters of 5–10
• on 2 cm long slender stalks
• mostly present from spring to autumn.

Fruit are:

• greenish-brown with red mottling
• circular and flattened
• 1–3 mm in diameter
• divided into 2 segments each with one seed.

Roots:

Roots form at the nodes along the long stolons at about 3–10 cm intervals.

Similar looking plants

Largeleaf pennywort (Hydrocotyle bonariensis) is a similar looking weed. This plant is very common and widespread in the Greater Sydney Region, especially in lawns. Its leaves are circular with shallow lobes and are up to 12 cm wide. The stem joins the leaf in the centre and the underside of the leaf is dull.

There are 17 species of Hydrocotyle in NSW. Most are native and include the following similar looking species:

• Hydrocotyle pedicillosa which has very hairy stalks and hairs on the leaf veins.
• Shield pennywort (Hydrocotyle verticillata) which has much smaller leaves (2–4 cm diameter)  

Where is it found?

Hydrocotyl does not currently grow in NSW. There are some infestations near Perth in Western Australia.

Hydrocotyl is native to the Americas, tropical Africa and Asia. It was brought to Australia as an aquarium and ornamental pond plant. Australia's first infestation was in 1983 near Perth. In 1992, a larger infestation covered one-third of the water along a 7 km stretch of the Canning River in WA. It is a serious weed in Europe, Britain, and Ireland and it has naturalised in South Africa.

What type of environment does it grow in?

Hydrocotyl prefers still or slow-moving fresh water in temperate climates. It will grow in rivers, wetlands, lakes and dams especially those with high nutrient levels. It can also grow on the edges of still water bodies. 

Maps and records

• Recorded presence of Hydrocotyl during property inspections (Map: Biosecurity Information System - Weeds, 2017-2023)
  These records are made by authorised officers during property inspections under the Biosecurity Act 2015. Officers record the presence of priority weeds in their council area and provide this to the NSW Department of Primary Industries. Records reflect the presence of the weed on the date of inspection.
  
  

How does it spread?

By seed

The fruit produces 2 seeds but only one is usually viable. Water spreads hydrocotyl seeds.

By plant parts

Hydrocotyl can re-grow from very small pieces of stem if they have a node. The fragments can be spread to new locations by flowing water, water birds and human activities such as boating.

References

Djeddour, D. (2017) CABI Invasive Species Compendium Data sheet: Hydrocotyle ranunculoides (floating pennywort). Retrieved 14 December 2014 from: https://www.cabi.org/isc/datasheet/28068

Hosking, J.R., Sainty, G.R., Jacobs, S.W.L., & Dellow, L.L. (in prep). The Australian WeedBOOK.

Hussner, A., Denys, L., van Valkenburg, J. L., & Warenautoriteit, N. V. E. (2011). Hydrocotyle ranunculoides NOBANIS–Invasive Alien Species Fact Sheet. Retrieved 22 march 2021 from: http://nora.nerc.ac.uk/id/eprint/19956/1/Hydrocotyle_State-of-the-Art.pdf

Queensland Government (2016). Weeds of Australia, Biosecurity Queensland edition Fact sheet: Hydrocotyle ranunculoides L. f. Retrieved 22/03/2021 from https://keyserver.lucidcentral.org/weeds/data/media/Html/hydrocotyle_ranunculoides.htm

Ramírez, C., Romero, M., & Riveros, M. (1979). Habit, habitat, origin and geographical distribution of Chilean vascular hydrophytes. Aquatic Botany, 7, 241-253.

Sainty, G. R., & Jacobs, S. W. (2003). Waterplants in Australia (No. Ed. 4). Sainty and Associates Pty Ltd.

back to top

Control

Please do not attempt to treat or dispose of this weed yourself. Report this plant if you see it anywhere in NSW by calling the helpline listed at the top of this page immediately.

NSW DPI will lead an initial response for the treatment and disposal of the plant to stop it from spreading.

Herbicide options

See Using herbicides for more information.

---

PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Only products registered for aquatic use)
Rate: One part product to 50 parts water
Comments: Spot spray
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

---

PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Only products registered for aquatic use)
Rate: One part product to 9 parts water
Comments: Splatter gun
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

---

back to top

Biosecurity duty

The content provided here is for information purposes only and is taken from the Biosecurity Act 2015 and its subordinate legislation, and the Regional Strategic Weed Management Plans (published by each Local Land Services region in NSW). It describes the state and regional priorities for weeds in New South Wales, Australia.

Area	Duty
All of NSW	General Biosecurity Duty All pest plants are regulated with a general biosecurity duty to prevent, eliminate or minimise any biosecurity risk they may pose. Any person who deals with any plant, who knows (or ought to know) of any biosecurity risk, has a duty to ensure the risk is prevented, eliminated or minimised, so far as is reasonably practicable.
All of NSW	Prohibited Matter A person who deals with prohibited matter or a carrier of prohibited matter is guilty of an offence. A person who becomes aware of or suspects the presence of prohibited matter must immediately notify the Department of Primary Industries

back to top

Reviewed 2021