Most Unwanted: Curly waterweed
Lagarosiphon major
Habitat: Freshwater
Threat: Clogs waterways and negatively impacts on native species and ecosystems
Status: Established
What is it
This species acts as an aggressive, invasive, alien plant species in Ireland but it is also regarded as a nuisance weed in its home territory. The leaves are strongly recurved and are borne in whorls of 3 or in a spiral arrangement. The long stem is brittle and easily broken (aiding dispersal). Only female plants are present and all reproduction is by fragmentation or vegetative reproduction.
Habitat
Lakes and slow flowing aquatic systems such as canals, low energy rivers and streams. The plant can grow in water up to 6m deep. In addition to occupying the full water column, plant stands produce dense vegetation on the water surface.
Impact
Currently, in Ireland, we are at an early stage in infestation; however, significant weed stands exist in Lough, Corrib. The plant forms very dense infestations in suitable habitats and is capable of occupying the full water column in waters up to 6m deep leading to significant changes to the ecology for native plants, insects and fish.
The species is a serious threat for tourism, angling, boating and other recreational pursuits as well as conservation goals.
Where is it from?
Originating from southern Africa but the species is now invasive in mainland Europe and Britain.
Where is it now
Present at a number of aquatic sites throughout the island.
How did it get here
Sold as an oxygenating plant in Garden Centres and aquarium supply outlets
How does it spread?
Spread by fragmentation via wind dispersal, boat movement, angling equipment and, possibly waterfowl. When detached stems sink they root from the nodes and establish new populations.
Additional reading
Habitas Invasive Alien Species in Northern Ireland
