Photo: Bob Luscombe – Hyde, Peak Forest Canal
Floating Pennywort (Hydrocotyle ranunculoides) is a species native to North America. It was first discovered naturalised in Essex in 1990 and had been introduced to the UK as an ornamental plant for ponds. Since April 2014 it has not been available to buy in the UK.
It is now common in the south-east of England and occasionally found in the north-west of England and Wales.
Floating Pennywort is found emergent or floating on still or slow moving waterways and prefers areas of full sunlight.
This plant can outcompete native species by blocking sunlight, reducing water temperature and preventing air-breathing insects from reaching the water's surface. It can deoxygenate the water by reducing available light to waterweeds and algae, then causing nutrient overload when it dies back.
Floating pennywort can grow up to 20cm a day forming dense mats of vegetation that quickly dominate waterways making navigation difficult and impeding water flow, also increasing flood risk.
Spreads easily via plant segments that break off and move through the waterways via currents or attached to boats. Roots form at the plant nodes, allowing it to quickly regenerate. During the summer it can double it's biomass between 4-7 days.
Floating pennywort is listed under Schedule 9 of 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.
Floating Pennywort should be reported via the Recording Native Species Counts scheme.
GB Non-Native Species Secretariat's Factsheet
You should record the presence of Floating Pennywort on a national database. This is easily done via the PlantTracker app, a recording system created in partnership with the University of Bristol, Environment Agency and the Centre for Hydrology & Ecology. Alternatively you can record online at the Non-native Species Secretariat website. You should also alert the appropriate land owner, council and or management body to the presence and location of this plant.