Quick Facts

Quick facts

  • Long-leaved Water Primrose (Ludwigia longifolia) spreads by seed and stem segments.
  • Once established, seedlings grow vigorously, forming tall, dense bushes that out-compete other species.
  • Long-leaved Water Primrose reduces the rate of flow in streams and may causes wide ecological damage by increasing sedimentation and decreasing oxygen levels.
  • Management should be focused on seedlings and the soil seed bank to control the source of dispersal before the rate of spread becomes too great.

What Does It Look Like?

What is it?

Long-leaved Water Primrose (Ludwigia longifolia) is an erect annual shrub which grows to 3 m tall. Its stems are hairless, 4-angled and much-branched towards the top. Younger stems are green or reddish in colour. The older branches become rounded and woody with age. The leaves are stalkless, hairless, glossy and alternately arranged along the stems. The leaves are lanceolate (much longer than broad, broadest near base, tapering to the apex) and 5-35 cm long and 4-25 mm wide. The flowers are single and yellow and found in the axils (the angle between leaf and stem) of the upper leaves. The flower stalks are 5-40 mm long and strongly four-angled. The flower has four green or red pointed sepals 10-18 mm long and 4 or 5 petals 20-25 mm long and 20-23 mm wide with prominent veins. The fruit is hairless and sharply four-angled 10-42 mm long and 4-8 mm wide with the 3 or 4 sepals persisting on the upper edge. Large numbers of tiny seeds less than 1 mm long are arranged in four sections. The fruit become light brown in colour as they mature and split open or disintegrate to release their seeds (The Weed Society of Queensland 2007; Harden 2007).

For further information and assistance with identification of Long-leaved Water Primrose contact the herbarium in your state or territory.

Flower colour


Growth form (weed type/habit)

Shrub, Aquatic

Where it currently grows? Preferred habitat

Long-leaved Water Primrose is a weed of waterways, wetlands, swamps, marshes, drains, channels and riparian areas (The Weed Society of Queensland 2007).

Are there similar species?

Ludwigia octovalvis, a native species, can be confused with Long-leaved Willow Primrose. This native species can be distinguished by the hairy stems, leaves and fruit, the almost round stems and cylindrical or only slightly ribbed fruit. Ludwigia peploides subsp. montevidensis, another native species, is also similar, but can be distinguished by its creeping habit and the fact that it usually has 5 petals and sepals (rather than 4 of Long-leaved Willow Primrose). Another introduced weedy species, Peruvian Water Primrose (Ludwigia peruviana), can also be confused with Long-leaved Willow Primrose. This plant is a serious weed in the Sydney region. Like Long-leaved Willow Primrose, Peruvian Water Primrose has strongly four-angled fruit, but it can be distinguished by its hairy stems, leaves and fruit and also by its shorter, broader leaves (The Weed Society of Queensland 2007; Harden 2007).

Why Is It A Weed?

What are its impacts?

Long-leaved Water Primrose forms very dense colonies and, if allowed to spread unmanaged, will dominate wetlands and riparian vegetation and will replace similar native species that grow in such environments (e.g., Ludwigia octovalvis). It is thought to be a potential pest in the tropical, sub-tropical and warmer temperate regions of Australia (particularly in the coastal districts of eastern and northern Australia). In Port Stephens it has been extremely invasive and has formed dominant colonies that have the potential to reduce biodiversity and threaten native species. Its dense growth also obstructs water flow and has the potential to reduce the use and enjoyment of aquatic habitats (The Weed Society of Queensland 2007).

How does it spread?

Long-leaved Water Primrose reproduces by seed and by branches which detach during floods, take root and develop into new plants. The small and numerous seeds can be dispersed by water, wind, animals, or human activities such as contaminated soil or dumped garden waste (The Weed Society of Queensland 2007).

What is its history in Australia?

Long-leaved Water Primrose was introduced to Australia as a garden ornamental and was first recorded as naturalised near Sydney in 1991 (The Weed Society of Queensland 2007).

How To Manage It?

Best practice management

Management of Long-leaved Water Primrose should focus on control of the seedlings and soil seed bank as it is important to control the major source of dispersal before the rate of spread becomes too great. Control of plants with herbicide or by physical means is effective but constrained by the nature of the wetland habitats and the prolific seedling growth (Port Stephens Council 2006). To manually remove the infestation, first carefully remove any seed heads and bag them securely in plastic bags. Mature fruits are easily spread causing long term land contamination and care should be taken not to inadvertently spread seed attached to clothing. Seedlings can be hand pulled, but larger plants will re-shoot unless the majority of the long root system is removed. Plant segments can resprout so incinerate or seal in plastic bags all plant parts to avoid further spread. Always follow up by rechecking the plant for any regrowth and the area for any new seedlings (Sydney Weeds Committee 2006).

To use chemical control scrape or cut and paint stems of mature plants with a herbicide. Treat or remove plants in spring and summer while actively growing before seed maturity and preferably before seed set (Great Lakes Local Council 2006).

There are no official biological control agents for Long-leaved Water Primrose in Australia, and the species is not currently a Target for Biological Control. However a native Flea Beetle (Altica sp.: Chrysomelidae) has been observed feeding on plants and potentially could be used to control infestations. Research into aspects of utilising Altica beetles for control is underway at several sites in Port Stephens (Port Stephens Council 2006).

Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au

Does it have a biological control agent?


When does it grow? (lifecycle/growth calendar)

Long-leaved Water Primrose flowers commonly during summer and autumn, but has been recorded as flowering at other times of the year. A mature plant can produce up to 2.5 million seeds per year (The Weed Society of Queensland 2007).

Where Is It Found?

Which states and territories is it found?


What areas within states and territories is it found?

Long-leaved Water Primrose has become a significant problem in the Port Stephens and Gosford areas on the New South Wales Central Coast. In more recent times it has also become increasingly common in the Sydney region, and there have been confirmed sightings in the Pittwater area since 2002. In the last couple of years a few small infestations have been found along a drain and a creek in Toowong in Brisbane. Additional infestations have recently been detected along several kilometres of Ithaca Creek in northern Brisbane (The Weed Society of Queensland 2007; AVH 2007; Harden 2007).

Where does it originate?

Long-leaved Water Primrose is native to South America (e.g., Brazil, Paraguay, Uruguay and north-eastern Argentina) and is considered a major weed within these areas (The Weed Society of Queensland 2007).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?


Where is it a declared weed?


Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?


Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?


Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Ludwigia longifolia

Other scientific names (synonyms)?


Does it have other known common name(s)?

Long Leaf Willow Primrose, Longleaf Willow Primrose, Longleaf Primrose Willow, Longleaf Ludwigia, Primrose Willow, Willow Primrose

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