Water primrose

Ludwigia grandiflora

Overview

Habitat: Still or slow flowing freshwater habitats

 

Description: Water Primrose is a perennial herb with powerful roots and stems that grow horizontally from the edges of the water body for 4 to 5 m. The species can grow vertically to about 1 m above the water surface making areas look like dry land.

The species can also grow from very small fragments allowing new infestations to become established easily. It is a vigorous aquatic plant with bright yellow, showy flowers and willow-like leaves.

 

Origin and Distribution: Native to South America and some US states. This species is now known in Britain where control measures are underway to prevent further spread and significant economic loss associated with this species. Ludwigia species have become naturalised in France where it has cost millions of Euro to the French economy. It was introduced in France in the 19th century as an ornamental plant but has since spread into nine Member States (Belgium, France, Germany, Hungary, Ireland, Italy, the Netherlands, Spain and the United Kingdom) where it thrives in slow flowing rivers, streams, lakes and ponds.

 

Impacts: Ludwigia grandiflora can form very dense (almost impenetrable) mats in freshwater ecosystems. Large accumulations of this species can lead to a depletion of oxygen levels in the water while also competing with native species for space and resources. It further releases chemicals that suppress other organisms (allelopathy), leading to the accumulation of toxins and the poisoning of entire water ecosystems. This species has been linked to significant losses in biodiversity at impacted sites in France. These not insubstantial and year-round effects on water quality can cause ‘dystrophic crises’ and intoxicated ecosystems (Dandelot et al., 2005). This is an economic pest as it can clog waterways, drainage streams, bathing waters, impedes boating and increases the risk of flooding.

 

Is it found in Ireland? Ludwigia grandiflora was identified in a series of isolated ponds on the south west coast of Ireland. The species is not yet found in the wild on the Island of Ireland.

How might it get into the wild Here? The aquaria trade and pond owners emptying their contents into the wild is the most likely pathway for introduction of Ludwigia grandiflora -  remember Be Plant Wise

 

EU-level action includes a ban on sales and on any planting or keeping, including in isolated ponds
Prevention
  • Promote native species and biodiversity - use alternative, native plants
  • Know what you are buying/growing and source native Irish seed and plants
  • Be Plant Wise - do not swap plants and cuttings with friends
  • Clean plants before adding to ponds (dispose of water away from water courses)
  • Follow control advice and watch out for hitchhikers - inspect new imported purchases for invasive pest and pathogens
  • Check Clean & Dry equipment before moving between water bodies
  • Never collect plants from the wild
  • Safe disposal of plant material and growing media

 

 

Images Courtesy of Q - bank and GBNNSS

Invasive Species Ireland

Invasive Species Ireland