Limnobium laevigatum
An opportunistic coloniser of open, shallow wetlands, ditches and creek banks
Family: Pontederiaceae
Origin: North, Central and South America
Habit: Perennial annual submerged or floating in shallow water (less than 15 cm deep), will grow to 50 cm tall and rapidly form dense mats in tropical and subtropical areas when not shaded by other plants
Leaves: Leaf blades arranged alternately along stems, 5 cm × 3 cm long, glabrous, obtuse or rounded at apex and bilobate at the base. Leaves are sessile, forming basal rosettes. The petiolate leaves can be floating or immersed.
Flowers: White to pale blue flowers 2–10 per raceme , open about three hours after sunrise and wilt by early afternoon
Fruit and Seeds: A capsule with 8–14 small winged seeds; long lasting
Roots: Roots stems produce roots at each node
Dispersal: Broken fragments of stems, with one or more nodes intact can infest downstream areas; floods can disperse stem fragments over a considerable distance. Winged seeds likely to be dispersed by wind and water.
Control: Please do not attempt to treat or dispose of this weed yourself. Report this plant if you see it anywhere in NSW by calling the NSW DPI Biosecurity Helpline 1800 680 244 immediately. NSW Department of Primary Industries will lead an initial response for the treatment and disposal of the plant to stop it from spreading


Adapts quickly to favourable situations such as recently inundated areas and areas where competition has been destroyed (including with herbicide use against other species). Hence in ponds and sinkholes, wet crop areas, ditches, powerline corridors. Long lasting soil seed banks give rise to seemingly spontaneous infestations.
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