Common names: Kariba weed (English); Watervaring (Afrikaans)
Origin: South America
Free-floating, perennial aquatic fern with horizontal stems forming mats up to 2 m thick. Leaves/fronds successively paired, oval to almost round, sometimes incised at the tip; surface bristly due to hair-like strands that join at the tip to form characteristic eggbeater shapes. A third, hairy frond modified to be root-like hangs in the water.
Commonly infests large areas of standing and slow-moving water, especially in reservoirs, lakes and marshes. Tolerant of a wide range of temperatures, it prefers nutrient-rich water and easily lives in polluted waters such as those high in nutrient runoff from fields, where it is capable of forming dense mats that reduce water-flow and lower light and oxygen levels in the water, resulting in stagnant, dark environments. This reduces biodiversity and abundance of freshwater species, including fish and submerged aquatic plants, altering wetland ecosystems and causing wetland habitat loss. Dense Salvinia invasions also threaten socio-economic activities that depend on open, flowing and/or high quality waterbodies, such as fishing and hydro-electricity generation.
Photo: "Salvinia molesta". Licensed under CC BY 2.5 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Salvinia_molesta.jpg#/media/File:Salvinia_molesta.jpg