There are 14 freshwater aquatic plants and 13 marine within the WCA for England & Wales. Many of the freshwater weeds have different growth habits: some growing entirely under the water (submerged) e.g. curly waterweed; others grow under the water but emerge at the surface (emergent) e.g. parrot’s feather; and some can be free floating e.g. water fern. There are also some species that are amphibious / marginal, and others that grow in all these situations e.g. New Zealand Pygmy Weed (Crassula helmsii). All these plants are highly invasive and can spread via fragments. Coupled with their growth habits these plants can be difficult to control, therefore management should focus on long-term control and biosecurity with complete eradication often being difficult.
New Zealand Pigmyweed
Crassula helmsii, or New Zealand Pigmyweed, is a perennial non-native invasive plant primarily found in the south of England, in freshwater habitats such as lakes, ponds, reservoirs and canals. It will tolerate differing PH levels, and even slightly salty water. It is native to the coastal regions of New Zealand, Tasmania and southern Australia, and is believed to have been first introduced to the UK in 1911.
Due to the extremely invasive nature of the plant, it is listed under Schedule 9 of the Wildlife and Countryside Act (1981) rev. 2, meaning it is an offence to plant or cause the spread of the species.
Floating Pennywort
Floating pennywort (hydrocotyle ranunculoides) is an invasive non-native aquatic species that can be free floating, or rooted; it is mostly prevalent in the south east of England, and has also been found in Wales and the north west of England, however it is native to North America. Its invasive nature means it is listed under Schedule 9 to the Wildlife and Countryside Act (1981) rev. 2, and as such, it is an offence to plant or otherwise allow the species to grow in the wild. The species was banned from sale in 2014.
Water Primrose
Water primrose (ludwigia grandiflora), an invasive non-native aquatic species, was originally introduced as an ornamental and water garden plant from South America, now listed under Schedule 9 to the Wildlife and Countryside Act (1981) rev. 2 due to its invasive nature. The species was banned from sale in 2014. It is most commonly found in still or slow-flowing water.
For more information and help in identifying these aquatic invasive species, please see our fact sheets located in the Advice & Guides section.
