Water hyacinth (Eichhornia crassipes) (Pontederiaceae)
The weed
Water hyacinth is frequently branded as the world’s worst aquatic weed due to its invasive potential, negative impact on aquatic ecosystems, and the cost it necessitates to control it. Originally a native of the Amazon basin, the weed has spread throughout tropical, subtropical and some warmer temperate regions of the world since the late 1800s. Water hyacinth is typified as an herbaceous, free-floating aquatic plant with erect aerial leaves, lilac flowers and submerged roots. Free-floating individual plants develop short bulbous petioles which are spongy, enabling the plant to float on the water’s surface. Once growth is sufficient to cause crowding of individual plants, these petioles elongate and interweave, forming dense self-supporting mats that can cover the entire surfaces of dams and slow flowing rivers.
Water hyacinth was first recorded in South Africa on the Cape flats in the early 1900s and since then, has spread throughout the country. This extensive distribution, as well as the resilience of the weed, is attributed to the highly eutrophic, or nutrient enriched, state of South Africa’s waters, and has led to the severe degradation of a number or aquatic ecosystems. Negative effects associated with water hyacinth infestation include the suppression of local aquatic biodiversity, the obstruction of river flows which may aggravate flooding and promote siltation, interference with water utilization for activities like recreation or irrigation, and increased rates of evapotranspiration from water storages. Infestation also poses a potential health risk in that the plant has been implicated in the creation of breeding habitats for malaria carrying mosquito larvae as well as other disease vectors such as the bilharzia snail. Due to these effects, coupled with the limited water resources available in South Africa, E. crassipes has been declared a category 1b weed in terms of the National Environmental Management: Biodiversity Act (10/2004): Alien and Invasive Species Regulations, 2014, which necessitates its control or eradication where possible.