Weed Alert: Hydrocotyl
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Contacts and Further InformationIf you find this weed please help to prevent its further spread by contacting your local Council Weeds Officer or the nearest NSW Department of Primary Industries office immediately for positive identification and further assistance.
Alternatively call the NSW Weeds Hotline on
1800 680 244 or send an email to firstname.lastname@example.org
Hydrocotyl (Hydrocotyle ranunculoides)
Hydrocotyl, also known as water pennywort, is an aquatic perennial plant that can rapidly form a dense mat in stationary or slow-flowing freshwater such as rivers, wetlands, lakes and dams.
The high growth rates and dense mats formed by hydrocotyl allow it to quickly replace native vegetation and reduce habitat for native fauna.
Originally introduced to Australia as an aquarium and ornamental pond plant, the first infestation was recorded in 1983 near Perth, Western Australia. In 1992 a more substantial infestation of hydrocotyl was discovered, which covered one third of the water surface along a 7 km stretch of the Canning River in Western Australia.
Hydrocotyl is currently found in coastal freshwater streams and water storages near Perth. It is potentially a serious weed of freshwater wetlands and other nutrient enriched watercourses throughout most of coastal Australia. No infestations have been recorded in New South Wales.
Hydrocotyl is native to the Americas, tropical Africa and Asia.
It has become a serious weed in Belgium, the Netherlands and England, Wales and Ireland following its introduction from the nursery trade in the 1980s, where it is believed it was wrongly labelled as the native species Hydrocotyle vulgaris.
Hydrocotyl has naturalised in South Africa and has spread into a number of other European countries including France, Germany and Italy.
Hydrocotyl spreads from stolons and the movement of plant fragments, fruit and seed along watercourses.
Hydrocotyl produces roots at every node and is capable of inhabiting a new site from broken plant fragments that travel downstream. It is fast growing and can spread hundreds of metres through stolon growth alone. In the United Kingdom it has been recorded growing up to 23 cm per day.
Seeds germinate in early spring on the muddy banks of water courses.
Hydrocotyl is a perennial hairless plant with long stolons. Roots are produced at each node and leaves float or emerge up to 40 cm above the water surface. The tangled mass of roots and leaf stems can sink up to 50 cm into the water.
Key identification features
- Leaves occur alternately along the stolons, are circular to kidney-shaped, up to 10 cm wide and contain 3–7 lobes with shallow-toothed edges. Each leaf stalk emerges from nodes along the stolon, is 2–25 cm long and attaches to the bottom of the leaf, close to the centre.
- Tiny greenish, yellowish or white five-petalled flowers (2–3 mm in diameter) occur below the leaf canopy in clusters of 5–10. Flower stalks are slender, about 2 cm long and arise from the nodes. Flowering occurs from spring to autumn.
- Fruit is almost circular, 1–3 mm in diameter and splits into segments.
Hydrocotyl is a highly invasive plant of waterways. If you suspect you have found hydrocotyl you should contact your local council weeds officer who will assist with identification, removal and eradication.
Hydrocotyl is a Class 1 State Prohibited Weed across NSW under the Noxious Weeds Act 1993. It must be eradicated and land must be kept free of the plant. As a notifiable weed, all outbreaks must be reported to the local council within 24 hours, and the plant is prohibited from sale in NSW.
Reviewed by: Charlie Mifsud, Rod Ensbey; Edited by: Elissa van Oosterhout, Birgitte verbeek
- CABI Invasive Species Compendium website—www.cabi.org/isc
- Hosking JR, Sainty GR, Jacobs SWL & Dellow LL (in prep) The Australian WeedBOOK