Floating Pennywort
Name: Floating Pennywort
Latin name: Hydrocotyle ranunculoides
Occurrence: Floating pennywort (Hydrocotyle ranunculoides) was brought to Britain in the 1980’s as a plant for tropical aquaria and garden ponds. However by 1991 it had become present in the wild.
Floating pennywort grows in shallow, slow-flowing eutrophic water bodies and forms dense interwoven mats of vegetation. These mats will quickly cover the water surface and can grow 20cm per day, resulting in a growth of up to 15m from the bank in a single season. This mat starves the waterbody of light, nutrients and oxygen which kills many of the species living in it and also increases the risk of flooding by blocking the waterway.
Facts and figures:
Native range: North America
Stem: Horizontal
Fleshy appearance
Leaf stalks and roots every 0.2-0.3m
Leaves: Circular or kidney-shaped
Deeply lobed
Up to 180mm across
Flowers: none
Persistence and Spread: Floating Pennywort can double its weight in as little as 3 days. In Britain the plant exhibits seasonal growth. Maximum growth occurs in late summer and it over-winters on banks as a much smaller and flatter plant.
New plants: Vegetative reproduction in Britain, and can form extensive mats from the smallest shoot fragment.
Management: Control is extremely difficult to control due to rapid growth rates but can be achieved using tailor-made treatment programs carried out by a specialist company.
Chemical control: can use glyphosphate or 2,4-D amine but plant does not rot down very quickly after treatment so vegetation should be removed after 2-3 weeks in flood risk areas. Regular treatment necessary throughout the growing season.
Regular cutting from May-October will prevent complete dominance. Cut material needs to be removed from the water immediately. Hand pulling or spot chemical treatment should follow cutting to reduce re-growth. Pulling can work well on small infestations.
