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Scientific Name
Synonyms
Family
Common Names
Origin
Cultivation
Naturalised Distribution
Habitat
Habit
Distinguishing Features
Stems and Leaves
Flowers and Fruit
Reproduction and Dispersal
Environmental Impact
Other Impacts
Legislation
Management
Similar Species
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Click on images to enlarge

habit (Photo: Sheldon Navie)

habit (Photo: Sheldon Navie)

elongated and hairless glossy leaves (Photo: Sheldon Navie)

close-up of four-angled, slightly winged, stem and leaves with reddish-coloured mid-ribs (Photo: Sheldon Navie)

close-up of flower with four broad yellow petals (Photo: Sheldon Navie)

young fruit with four large persistent sepals (Photo: Sheldon Navie)

immature, four-angled, hairless fruit (Photo: Sheldon Navie)

mature fruit releasing their numerous tiny seeds (Photo: Sheldon Navie)

seedlings (Photo: Sheldon Navie)

comparison of the seedlings of native willow primrose (Ludwigia octovalvis), on the left, and long-leaved willow primrose (Ludwigia longifolia), on the right (Photo: Sheldon Navie)

native willow primrose (Ludwigia octovalvis), with round hairy stems and hairy leaves (Photo: Sheldon Navie)

Ludwigia longifolia

Scientific Name

Ludwigia longifolia (DC.) H. Hara

Synonyms

Jussiaea longifolia DC.

Family

Onagraceae

Common Names

longleaf primrose willow, longleaf primrose-willow, longleaf willow primrose, long-leaved willow primrose, primrose willow

Origin

Native to South America (i.e. southern Brazil, Paraguay, Uruguay and northern Argentina).

Cultivation

This species was introduced as a garden ornamental for aquatic situations, though it is not common in cultivation.

Naturalised Distribution

Naturalised in the coastal districts of central and northern New South Wales and in south-eastern Queensland.

Also naturalised overseas in south-eastern USA (i.e. Florida).

Habitat

Long-leaved willow primrose (Ludwigia longifolia) is currently a weed of waterways and wetlands (e.g. swamps, marshes, drains, gullies, channels and riparian vegetation) in the warmer temperate and sub-tropical regions of Australia. It also has the potential to spread further northwards into tropical regions.

Habit

A small upright (i.e. erect) shrub or large herbaceous plant usually growing 0.5-2 m tall, but occasionally reaching up to 3 m in height. It can be short-lived (i.e. annual) or relatively long-lived (i.e. perennial).

Distinguishing Features

Stems and Leaves

The stems are hairless (i.e. glabrous) and are usually much-branched towards the top of the plant. Younger stems are green or more often reddish in colour (especially when growing in a sunny position), conspicuously square in cross-section (i.e. quadrangular), and usually also somewhat winged. However, they become rounded and somewhat woody with age and may eventually develop a reddish-brown coloured bark.

The leaves are alternately arranged along the stems and do are stalkless (i.e. sessile). They are hairless or almost hairless (i.e. glabrous or sub-glabrous) and have a somewhat glossy appearance. These leaves (5-35 cm long and 4-25 mm wide) are relatively long and narrow in shape (i.e. lanceolate) with pointed tips (i.e. acute apices) and entire margins. The central vein (i.e. midrib) of the leaf is prominent and often reddish in colour, like the younger stems.

Flowers and Fruit

The bright yellow flowers are borne singly in the upper leaf forks (i.e. axils) on stalks (i.e. pedicels) 5-40 mm long. Each flower has four greenish or reddish sepals (10-18 mm long) that have pointed tips (i.e. acute apices). These sepals enclose the petals when the flower is in bud and remain on the fruit as it develops (i.e. they are persistent). Each flower also has four, or rarely five, bright yellow petals (20-25 mm long and 20-23 mm wide) that readily fall off. These petals are broad with rounded tips (i.e. obtuse apices) and narrow bases. They also have relatively prominent spreading veins. Eight, or rarely ten, fluffy yellow stamens (6-8 mm long) are present at the centre of the flower, as well as a short style (3-5 mm long) that is topped with a relatively large stigma (4-6 mm long and 2-2.5 mm across). Flowering occurs throughout the year, but is most common during summer and autumn.

The fruit is a hairless (i.e. glabrous) and sharply four-angled capsule. These fruit (10-42 mm long and 4-8 mm wide) contain large numbers of tiny dust-like seeds (less than 1 mm long) in four internal compartments. They turn from green to light brown in colour as they mature, and eventually split open or disintegrate to release their seeds. The tiny seeds (0.5-0.8 mm long and 0.2-0.3 mm wide) are brown to yellow in colour, oblong in shape, and may be straight or curved.

Reproduction and Dispersal

This species generally only reproduces by seed, however branches that are detached during floods can take root and develop into new plants. The small seeds can be dispersed by water, wind, animals or human activities (e.g. in contaminated soil or dumped garden waste).

Environmental Impact

Long-leaved willow primrose (Ludwigia longifolia) is regarded as an environmental weed in New South Wales and as an emerging environmental weed in south-eastern Queensland. It was also recently listed as a priority environmental weed in two Natural Resource Management regions. This species can form very dense colonies and if allowed to spread unmanaged it can dominate wetlands and riparian vegetation, replacing native species that grow in such environments. Because of its invasiveness and ability to form dense single species populations, it is considered to be a major weed within its native range.

Long-leaved willow primrose (Ludwigia longifolia) was first recorded as naturalised near Sydney in 1991. Since then it has become a significant problem in the Port Stephens and Gosford areas on the New South Wales Central Coast. In the Salamander Bay area, at Port Stephens, it has been extremely invasive and has formed dominant colonies that have the potential to reduce biodiversity and threaten native species. In more recent times it has also become increasingly common in the Sydney region (e.g. there have been several sightings in the Pittwater area since 2002).

In the last couple of years this species has also become increasingly common around Brisbane in south-eastern Queensland. A few small infestations have been found along a drain and a creek in Toowong and larger infestations are also present along Ithaca Creek in Ashgrove and Kelvin Grove.

Long-leaved willow primrose (Ludwigia longifolia) is still in the early stages of its spread throughout the coastal districts of eastern Australia. It is thought to have the potential to become a problem species throughout the wetter tropical, sub-tropical and warmer temperate regions of Australia.

Other Impacts

The dense growth of long-leaved willow primrose (Ludwigia longifolia) also obstructs water flow and has the potential to reduce the usefulness and enjoyment of public aquatic areas.

Legislation

This species is declared under legislation in the following states and territories:

Management

For information on the management of this species see the following resources:

Similar Species

Long-leaved willow primrose (Ludwigia longifolia) is very similar to Peruvian water primrose (Ludwigia peruviana) and native willow primrose (Ludwigia octovalvis) and relatively is similar to water primrose (Ludwigia peploides subsp. montevidensis). These species can be distinguished by the following differences: