Long, lance-shaped leaves cover winged, upright, reddish stems growing 1- 2 metres tall. Younger stems are green or more often reddish in colour (especially when growing in a sunny position) and they are conspicuously square in cross-section. These sharply four-angled stems are usually also somewhat winged. However, they become rounded and somewhat woody with age and may eventually develop bark that is reddish-brown in colour.

Photo: Sheldon Navie
Flower closeup

Photo: Sheldon Navie
Foliage and immature fruit (persistent sepals)
Propagation is mainly by seeds although branches can take root and develop into new plants. Seeds are <1mm in size and dispersed by wind, water, human activity, birds and other animals. Seed densities of 25 million per m2 have been calculated. There is a native species of willow primrose Ludwigia octovalvis that can be easily confused with long-leaved willow primrose. This native plant also grows in wetter habitats and is widespread and relatively common in eastern and northern Queensland. Two distinct forms of this species, a broad-leaved form and a narrow-leaved form, are often encountered (sometimes growing together at the same site). However, both forms of this native species can be distinguished from long-leaved willow primrose by their hairy nature (i.e., hairy stems, leaves and fruit), their almost round stems, and their cylindrical or only slightly ribbed fruit.

Photo: Robert Whyte
Dried fruiting body releasing small seeds
Trees will reduce the growth of Ludwigia longifolia by providing shade and competition.
Correct disposal is essential due to the abundant seeds. All plants should be carefully handled and the fruit / seeds bagged. Vehicles and equipment are likely to contaminate new areas unless cleaned thoroughly.
Sources include: Graham Prichard 2004, Port Stephens Council Weed Information Sheet and the Weed Society of Queensland www.wsq.org.au

Photo: Robert Whyte