The diversity of the vegetation communities appearing in six floodplain sites of national importance along the Sarine River is presented. The site of Rossens, which is the most diverse, has been chosen to apply the methodology of the integrated synusial phytosociology which considers several spatio-temporal organizational levels. The synusiae of seven phytocoenoses are described. Using floristic and ecological comparisons, their integration in higher organizational levels (tesela, catena) is discussed.