EUPHRESCO DeCLAIM Final report. A State-of-the-art June 2011. Hydrocotyle ranunculoides L.f.

This report contains the result of research on Hydrocotyle ranunculoides and was part of a larger project EUPHRESCO DeCLAIM (Decision Support Systems for ControL of Alien Invasive Macrophytes). A project initiated to generate a prototype decision support system for optimal control measures for the four most troublesome invasive alien aquatic weeds at present in the UK and NL. Cabomba caroliniana, a representative for the Myriophyllids growth form, representing 35% of the import volume of aquarium plants in The Netherlands. In 2009 it was found at three sites in The Netherlands, posing serious problems at one. Hydrocotyle ranunculoides, a representative for the Stratiotids s.l. growth form, is at present the most troublesome invasive alien aquatic weed in the United Kingdom and The Netherlands, and is showing increased distribution in neighbouring countries as well as in the Australia, Uganda and Zimbabwe. A second representative for the Stratiotids s.l. growth form, Ludwigia grandiflora, has demonstrated significant detrimental ecological impact in France and is gaining importance in The Netherlands. In the UK early intervention management strategies using herbicides have been developed and deployed (DEFRA website). A third representative of the Stratiotids s.l. growth form is Myriophyllum aquaticum. This species has been sold extensively by the aquatic nursery trade as an ornamental species for domestic ponds. It is now present in many natural lowland static water sites in the UK. The species is still very popular in The Netherlands, and the number of infestations is increasing. The overall project was a joint effort between four partners. Plant Protection Service Plant Research International, Wageningen UR Aquatic Ecology and Water Quality Management Group, Wageningen UR Aquatic Plant Management Group, Centre for Ecology and Hydrology‐ Wallingford