International audience1. Aquatic ecosystems are currently invaded by non-indigenous aquatic plants. A major challenge for biologicalinvasion research is to develop the ability to predict the spread of species. 2. Throughout the world, Ludwigia peploides subsp. montevidensis and Ludwigia grandiflora subsp. hexapetala are now considered to be two of the most invasive aquatic plants. This paper reviews the scientific knowledge about these species, their ecological and socio-economic impacts and methods of management. 3. Water primrose possesses some advantageous biological traits, such as rapid growth rate, efficient reproductive capacity, high plasticity in growth response, broad ecological tolerance and allelopathic compounds which might explain its expansion and colonization of numerous ecosystems. 4. Much attention must be paid to Ludwigia grandiflora subsp. hexapetala and Ludwigia peploides subsp. montevidensis. According to climatic models, global warming will further increase the spread of these species in Europe

The paper presents a new index for assessing water trophy and organic pollution. It is based on only true aquatic macrophytes -being calculated on species score, coefficient of ecological amplitude and degree of cover. The method was tested in an acidic lowland river and an alkaline mountain river, and is shown to be validated by bio-indication scales based on macrophyte communities. The practical interest is discussed regarding the Water Framework Directive.

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