Rare and new Gomphonema Ehrenberg species (Bacillariophyceae) from northern Nouvelle-Aquitaine region (southwestern France)

Regular monitoring of the diatom flora as part of the biomonitoring of French rivers has highlighted the remarkable species richness of Gomphonema in the Nouvelle-Aquitaine region, southwestern France, and especially in the north, in the former Limousin region. This taxonomic study is based on detailed analyses using light and scanning electron microscopy. It describes six new species of Gomphonema and also highlights three other species rarely observed in French rivers and lakes. The emergence of new species should be explained both by the focus on understudied lentic environments and by the misidentification of species included in Gomphonema species complexes during routine exercises. We compare the new taxa with the most morphologically similar species of Gomphonema and demonstrate unambiguously that these new species possess a unique set of taxonomic features not observed in any other taxon. The assignment to a complex of Gomphonema species is also mentioned, including, more specifically, the species complex of G. clevei, G. entolejum, G. gracile and G. parvulum. Particular attention is paid to the description of the cingulum of Gomphonema dordoniense sp. nov. whose structure is highly unusual. In addition, we provide detailed ecological characteristics for each of these new species, including their sensitivity to major physico-chemical descriptors.