Family: Onagraceae

Status:

Description:
A large herb rooted at the water’s edge and growing out as a floating mat over the water. Mats may become free-floating. Stems are up to 3m high, branching and woody. Leaves are deciduous in winter in Sydney but evergreen further north. They are oval, 5-10 cm long, with deeply impressed regular veins and are finely hairy. The flowers are large (2-4cm diameter) mostly with 4 yellow petals (rarely 5 or 6). Seed is carried in a brown capsule to which the 4 rusty red sepals remain attached, forming a conspicuous star shape.

Preferred habitat and impacts:
Edges of fresh water bodies, preferably still.
Ludwigia can blanket the water surface reducing light levels, temperature and oxygen in the water below. This has profound effects on communities of native plants and animals in the water. Can also interfere with animal access for drinking water, human access for swimming and boating, reduce water quality and block pumps.

Dispersal:
Dispersal is mostly by seed, which sticks to wet surfaces and can be spread on birds and other animals, people, machinery and in mud or water.

Look-alikes:
Similar plants are other Ludwigia species, mostly also aquatic and introduced, but less invasive. A small species of water primrose (Ludwigia peploides ssp montevidensis) is sometimes regarded as native, or may be an introduction from South America. It is a small plant with similar flowers, which grows on the edge of water bodies. It is regularly encountered in south coast wetlands, but seldom in large amounts

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Control
If you suspect you have an outbreak of ludwigia, notify your local weed control authority (usually Council) and take their advice on control methods.
Ludwigia is less tolerant of dry soil than alligator weed, so lowering the water level in the water body, if feasible, may help to eradicate infestations. Herbicides are effective but repeated application may be needed.