Floating pennywort (Hydrocotyle ranunculoides) is an invasive aquatic plant which is native to North America. It was first brought to Britain in the 1980’s to sell as a plant for tropical aquaria and garden ponds.
Floating pennywort spreads rapidly from small root fragments and forms dense interwoven mats of vegetation. It can completely cover the surface of slow flowing rivers, streams, ditches, dykes lakes and ponds. Once established this plant causes significant impacts on the ecology, hydrology and amenity uses of the water body. During ideal conditions established colonies have been recorded growing up to 20 cm per day!
Floating pennywort is listed under Schedule 9 to the Wildlife and Countryside Act 1981 with respect to England, Wales and Scotland. As such, it is an offence to plant or otherwise cause this species to grow in the wild.