This spongy perennial resembles a small, floating, open head of lettuce.
Leaves are a floating rosette of pale green, fan shaped and covered with hairs. The leaves are up to 14 centimetres long and 8 centimetres wide.
Flowers when mature the plants produce lots of small, green flowers in their centre, between 7 to 12 millimetres long. A membrane separates the male and female flowers.
Fruit resembles a berry, 5 to 8 centimetres wide.
Seeds are small and oblong and are tapered at each end.
Roots are unbranched tufts and fibrous up to 80 centimetres long.
Habitat water lettuce prefers nutrient rich, stationary water bodies or slow moving streams.
Weed characteristics it rapidly forms dense mats covering rivers, dams and irrigation channels. It interferes with irrigation and stock watering, and large infestations can damage wildlife habitats and put children and livestock at risk if they become entangled in the roots. It can restrict water flow, increase water loss by transpiration and serve as a breeding ground for mosquitoes.
Dispersal it spreads both by vegetative reproduction and by seeds.
This species is a Class 2 declared plant under Queensland legislation.
How to act
Prevention is the best control method. Control of nutrient inputs into waterways will reduce rate of infestation. Early detection and rapid response will provide the best chance of control. Integrated control combining mechanical, biological and chemical methods with long term monitoring and follow up is required. Hand removal of small infestations is recommended. Biological control agents have proven to be effective throughout eastern Queensland. Apply herbicide strictly as per label recommendations.
Refer to Weed Control Methods.
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