This floating perennial water weed has a black root system and erect stems that can reach up to 1 metre long when the plant is fully matured.
Leaves are dark green rounded and waxy up to 5 centimetres wide. Leaf stalks are 5 to 20 centimetres long and are swollen into spongy, bulbous dense clusters.
Flowers are light purple with a darker bluish-purple and yellow centre. They are up to 4 centimetres long on dense spikes that are 50 centimetres long, with 3 to 15 flowers per spike. It flowers during summer and autumn.
Fruit are 3 celled capsules with small seeds that are viable for 15 years.
Habitat it prefers water with high nutrient content such as areas contaminated by sewage plant outflow and washings from stockyards.
Weed characteristics it invades creeks, rivers and dams as dense mats spread across water surfaces and infestations can double in size every week under ideal conditions. It destroys native habitats, depletes water bodies of oxygen, increases water loss and provides a breeding ground for mosquitoes. Stock may have difficulty accessing drinking water.
Dispersal it grows from seed and through vegetative reproduction.
This species is a Class 2 declared plant under Queensland legislation.
How to act
Prevention is the best control method. Early detection and rapid response will provide the best chance of control. Control of nutrient inputs into waterways will reduce rate of infestation. Integrated control combining mechanical, biological and chemical methods with long term monitoring and follow up required. Hand removal of small infestations is recommended, with ongoing monitoring and follow up required due to persistent seed viability. Biological control agent is effective in reducing plant vigour but does not provide complete control. Apply herbicide strictly as per label recommendations.
Refer to Weed Control Methods.
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