Two new Navicula species (Bacillariophyceae) from Western Europe

International audienceDuring a survey of some springs in the French Central Massif, a new Navicula species (Bacillariophyceae) was found:Navicula sanctamargaritae Beauger sp. nov. A second new Navicula species was observed during a routine biomonitoringproject in Flanders: Navicula flandriae Van de Vijver & A.Mertens sp. nov.. The new species are formally described usinglight and scanning electron microscopy. Both species present a unique set of morphological characters including the structureof the central raphe endings, the striation pattern, the valve dimensions and outline, which allows their separation fromsimilar Navicula taxa such as N. korzeniewskii, N. recens or N. cincta. The ecological preferences of each species are brieflydiscusse