aggressive introductions

example: floating pennywort

Here is an example of how a non native plants can cause problems once in the wild environment. Floating Pennywort (Hydrocotyle ranunculoides) is a sub-tropical plant originally introduced as a outdoor pool plant., which has escaped domesticity and established itself in over 40 of our more tranquil wild waters.

A single fragment snapped from the dense root mass can float away and grow at up to 20 cm a day to establish a new green mat elsewhere.

The plant causes de-oxygenation of the underlying water, killing fish and invertebrates. Most seriously Floating Pennywort out competes native plants such as frogbit, duckweed, and water crowfoot, and is seriously decreasing the nature conservation of some of our most beautiful and important wetlands.

floating pennywort photo

Since the plant spreads primarily through fragmentation, physical removal is a risk.: one square metre of pennywort weighs a huge 75 kg, because of the dense roots. Herbicides have been used by the centre for aquatic plant management in Sonning, Berkshire where pennywort has survived spraying with 2,4-D, but may have met its match with diquat. While in the short term it may also affect a few water plants not crowded out by pennywort and re-create the conditions for the native species to return.

If you spot any floating pennywort, please report any sightings to Jonathan Newman, The Centre for Aquatic Plant Management Tel: 01189 690072, E-mail: