In the United Kingdom it is an invasive alien species which is currently spreading in waterways. It was one of five aquatic plants which were banned from sale in the UK from April 2014, and was the first prohibition of its kind there. Water pennywort is also a weed in Australia. On the other hand, it is a threatened species in parts of its native range in the United States.
Water pennywort has stems that spread horizontally and can float on water. Leaves grow on petioles up to 35 cm long, and are round to kidney-shaped, with 3–7 lobes and crenate to entire margins. Flowers are small, pale greenish white to pale yellow, and come in umbels of 5–13. Fruits are small achenes that can float, helping the seeds to disperse.
- "Invasive non-native species - indicator two". Environment Agency. Archived from the original on 13 May 2010. Retrieved 28 August 2017.
- "Aquatic invaders threat to biodiversity". The Ecologist. Retrieved 2017-08-28.
- Kinver, Mark (2013-01-29). "UK bans sale of five invasive non-native aquatic plants". BBC News. Retrieved 2017-08-28.
- "Plants Profile for Hydrocotyle ranunculoides (floating marshpennywort)". plants.usda.gov. Retrieved 2017-08-28.
- "Water Pennywort". Retrieved 16 December 2012.
- "H. ranunculoides". Jepson Manual. University of California. Retrieved 16 December 2012.
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