Alternative common names:
Esthwaite waterweed (English)
Hydrilla is a submerged perennial aquatic plant with branching stems up to 2m long, but in deep water can reach 7m. It forms dense submerged masses which impacts on recreational activities such as boating and fishing. It also threatens indigenous aquatic plants. It looks similar to indigenous Lagarosiphon and would need to be examined microscopically.
Where does this species come from?Suspected to originate from the warmer parts of Asia.
What is its invasive status in South Africa?NEMBA Category 1a
Where in South Africa is it a problem?Pongolapoort (Jozini) Dam in northern KwaZulu-Natal.
How does it spread?Reproduces from seeds and two types of specialised buds. It can also propagate from fragments of the stem. Boats and fishing gear could spread this weed from Pongalpoort to other dams and rivers.
Why is it a problem?
It crowds out other aquatic plants. It hinders recreational boating, fishing and even makes swimming dangerous.
What does it look like?
Leaves: Leaves grow in whorls of 3-8 and have distinctly serrated margins. Leaves are usually 12mm long and 2mm wide and grow on long submerged stems up to 2m long.
Flowers: Inconspicuous, about 3mm across, at the tip of long thin stalks and float on the surface.
Fruit/seeds: Rounded capsule.
Does the plant have any uses?
Sometimes used for ornamental purposes in aquariums and ponds.