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.
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.
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 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
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
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.
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State Prohibited Weed
The plant must be eradicated from the land and that land must be kept free of the plant