During a floristic survey of freshwater lakes in the French Grand Est region, a new Sellaphora species (Bacillariophyceae) was found. Its morphology was examined in detail using light and scanning electron microscopy to formally describe it. Sellaphora davoutiana sp. nov. has elliptic-lanceolate valves with broadly protracted, subcapitate apices. Based on available literature, it is compared to morphologically similar species such as Navicula detenta, S. sardiniensis, S. sassiana and S. smirnovii. Valve dimensions, central area shape and striae density and pattern of this new species allow its separation from them. Sellaphora davoutiana has been found in three low-mountain lakes of glacial origin in Northeastern France, with watershed on granitic substratum. Additionally, illustrations of Hustedt type material of Navicula detenta are provided, and this taxon is formally transferred to the genus Adlafia.