A recent paper by Geoffrey Howard, Mike Bingham and Mark Hyde published in the journal BioInvasions Records flags up the risk of yet another invasive water plant species reaching the Kafue river basin and highlights the need for more records to monitor its spread and assess the threat to native wildlife.
The plant of concern is the Amazon Frogbit or South American Spongeplant Limnobium laevigatum (Humb. & Bonpl. ex Willd.) Heine (Hydrocharitaceae), a native of South and Central America that superficially looks like water hyacinth (Eichhornia crassipes (Mart. Solms)(Pontederiaceae).
The first reports from Africa were between 2009 to 2012, when plants were discovered in wetlands and water bodies near Harare and then at the edge of Lake Kariba and on the Zambezi river further downstream. Some plants were also found in an outlying population near Kasama in the Northern Province of Zambia. To date it has not been found in the Kafue river basin.
Most likely to have been introduced through the aquarium trade, the Amazon Frogbit has also become invasive in other parts of the World, notably Australia and North America, crowding out other water plants and blocking channels as well as shading out submerged plants and aquatic animals that need light to thrive.
The name “spongeplant” refers to the spongy surface on the underside of its leaves. This increases buoyancy so that the plant can easily float and move with the wind and water current. It may also move upstream and to new water bodies carried by boats and fishing gear or wildlife. Superficially like water hyacinth, plants may be emergent, with roots, or entirely free-floating.
The paper flags up the need for more records to help assess the speed and dangers of invasion. The similarity in appearance to water hyacinth may mean it has been overlooked and be far more widespread than present records suggest. The Trust would welcome any geo-referenced photographic records from the region. Please send them to firstname.lastname@example.org.
Reference: Geoffrey W. Howard, Mark A. Hyde and Mike G. Bingham, 2016. Alien Limnobium laevigatum (Humb. & Bonpl. ex Willd.) Heine (Hydrocharitaceae) becoming prevalent in Zimbabwe and Zambia BioInvasions Records, 5, 4: 221-225.