Riella (Riellaceae, Sphaerocarpales) is a genus of aquatic liverworts with disjunct range in areas of Mediterranean-type climates. Riella has been traditionally subdivided into two subgenera, subgenus Riella, whose plants show smooth or papillose female involucres and Trabutiella, whose plants show winged female involucres. To date only three species of Riella are known in France, all belonging to subgenus Riella. During the course of a study of the plant diversity of temporary brackish ponds in the Camargue area (Southern France), soil sediments were collected from 10 localities and cultivated in the laboratory. From cultures of five of these localities emerged dioicous plants of Riella showing winged female involucres that unambiguously assigned them to subgenus Trabutiella. The study of those specimens with Light and Scanning Electron Microscopy allowed us to identify them as R. cossoniana var. cossoniana. Fresh materials allowed for detailed morphological analyses on these new French materials which were fully described and illustrated. These findings represent the first report of a species belonging to subgenus Trabutiella from France and the second European country where R. cossoniana is reported. Four nearby populations occur within the perimeter of the Tour du Valat Regional Natural Reserve, and another in the industrial polygon of the Grand Port Maritime de Marseille.