The problem of invasive water hyacinth in Gauteng’s waterways is well-known, but environmental scientists are also concerned about the rise of other invasive aquatic plants.
Aquatic plants are plants that have adapted to living in water. They are also referred to as hydrophytes. These plants require special adaptations for living submerged in water, or on the water’s surface. Aquatic plants can only grow in water or in soil that is permanently saturated with water.
The Yellow water lily (Nymphaea Mexicana) is an aquatic plant with bright yellow flowers. Leaf blades and flowers appear above the water level, while the leaves with wavy margins spread on the water surface. The yellow flowers open during the day and close at night. It grows in marshes and readily invades canals and other shallow waterways, and is now regarded as the most invasive of the introduced water lilies in South Africa.
These lilies can form spreading colonies along riverbanks and other water bodies to a depth of about 3 m. Unlike the indigenous Nymphaea species, they are not adversely affected by the cold Highveld winters. They have invaded the Vaal River, lakes and dams, including Hartbeespoort Dam.
There are also hybrids, which have paler yellow flowers and which are also invasive.
They invade wetlands where they have become a noxious weed. They choke out native plants, slow water flow and can also stop all recreational use of the waterway.
Another problem plant is Water poppy (Hydrocleys nymphoides). It is a floating aquatic plant with heart-shaped leaves and delicate light-yellow flowers with three-petals. This tropical American plant can compete with indigenous water lilies and large infestations can block out sunlight to the detriment of other aquatic organisms.
There are indigenous species of Nymphaea which can successfully be used in one’s pond. There is N nouchali, which is the most widespread species, with flowers opening during the day and usually blue, but also shades of pink, mauve and white. Then there is Nymphaea lotus, the white water lily, or white lotus, which has night-blooming white or cream flowers.