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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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The longitudinal changes of richness and composition of aquatic plants have been studied from headwaters to the fifth stream order in three rivers in western Brittany (France), the Orne, Sélune and Rance. All rivers are regulated by dams along their lower reaches. The total macrophyte richness differed between the rivers (61 to 150 taxa); it was lowest in the Sélune, which flows over a granite substratum throughout its basin. Absolute richness per site varied greatly between rivers, and between groups of sites either upstream or downstream of the dams, though consistently higher values were observed downstream. In contrast, the relative richness at the river basin scale was similar for the group of upstream (average 20 taxa) and downstream sites (average 28) of all rivers. At the site level, richness increased along all there rivers. Several sites below the dams had the highest richness per site, with more than 40 taxa. A shifting evolution of the macrophyte richness was revealed along the river axis, related to habitat heterogeneity and geological changes.Of the 27 abiotic variables initially considered for canonical correspondence analysis, only five to six per river were retained by a forward selection procedure. The eigenvalues of the first two canonical axes explained 16.1 to 22.4% of the total biological variability and 53.9 to 67.7% of the species-environment relationships. The macrophyte distribution was mainly determined by the stream hierarchy, expressed by the distance to source and slope, and showed also the influence of regulation, i.e. the position of the site in relation to the dam. Other physical variables significantly contributed to plant distribution, namely particular habitat types, depth and geological substratum. Nutrient enrichment and organic pollution influences were the main secondary gradients for the Orne and Rance rivers.

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Fruit-set and seed-set depend on environmental conditions and reproductive systems. They are important components of sexual reproductive success in plants. They also control the ecological success and adaptation of invasive plants within their nonnative ecosystems. We studied which factors bring about fruit-set and seed-set in invasive populations of the aquatic plant Ludwigia grandiflora subsp. hexapetala. We analyzed fruit set and seed set in 37 populations growing under variable climatic conditions in Western Europe. Sub-samples of seven fruitful and fruitless populations were grown in common controlled conditions. We carried out self-and crosspollinations, and measured the floral morphometry. Environmental conditions did not affect fruit-set and seed-set in-situ and in common controlled environments. Handpollinations showed that individuals from fruitful populations exhibited fruit and seed production whatever the pollen donor, whereas individuals from fruitless populations only did so when pollen came from fruitful populations. Floral morphometry evidenced the existence of two floral morphs that fully overlapped with fruitfulness, and individual incompatibility. Our results rebutted the hypothesis that environmental variations control fruit set and seed set in these invasive populations. We instead showed that fruit set and seed set were controlled by a heteromorphic reproductive system involving a self-incompatible and inter-morph compatible morph (long-styled morph), and a self-and inter-morph compatible reverse morph (short-styled morph).We collected morphs and fruit set records of this species worldwide and found the same relationship: fruitless populations were all composed only of individuals with long-styled floral morph. Our study constitutes the first evidence of a heteromorphic self-incompatible system in Ludwigia genus and Onagraceae family. K E Y W O R D Sheteromorphic self-incompatible system, freshwater invasion, climate impact, management plan, Ludwigia grandiflora subsp. HexapetalaThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Biological elements, including phytoplankton, phytobenthos, macrophytes, benthic invertebrates and fish, are employed by the EU Water Framework Directive (WFD) 2000/60/EC as ecological indicators for the assessment of surface waters. The use of primary producers (phytoplankton, phytobenthos and macrophytes) for water quality assessment has a long history, and several methods have been developed worldwide. In this study, we used these three communities to assess the ecological status of five natural lakes located in the Aquitaine region (southwest France). Several biological indices used in lakes from other European countries or in French rivers were employed and compared among the three communities. Each primary producer provided complementary information about the ecological status of the lakes, including the invasiveness of exotic taxa. Regardless of the producer community used, the response to the environment, as reflected by the indices (adequate for each community), was similar: Lakes Cazaux, Lacanau and Hourtin showed the best ecological status and Parentis and Soustons the worst. Phytoplankton diagnosis reflected and integrated unambiguously the water quality of the lakes, as demonstrated by the strong relationships between the phytoplankton index and the trophic status criteria. This community appeared as the best indicator, especially when macrophytes were absent. The methods applied here represent a potential tool for the assessment of the ecological status in the context of WFD, but they need to be refined. We propose modifications for phytobenthos index initially tailored for running waters for adequate use in lentic ecosystems. Indices for the three primary producers should be modified to incorporate exotic species which may provide information on potential biodiversity losses.