The riparian flora of the upper part of the river Weser, about 200 km long, was recorded between Münden and Minden. 42 representative sections each in a distance of 5 km to each other were mapped. For recording the stock of species as completely as possible further parts of the river banks were investigated by spot-checks. Altogether 236 vascular plant species were found. For 196 of these species the frequency distribution is pointed out. The plant communities of the river banks are described by sociological releves. Despite the relatively high similarity of the investigated sections, manifested by 32 high frequent species, the data allow to divide this part of the river Weser into 3 sectors by floristical aspects. For each sector the frequency of the river bank species are stated. By reasons of the high salt content of this part of the river Weser 20 species which are at least weakly salt tolerating are to be found, predominantly in the upper sector. Obviously the more salt tolerating taxa are receding, caused by the decreasing salt content. In a whole 36 neophytes were found on the river banks of this part of the Weser, the spreading of which occurred in general in this Century. Most frequent species are Bidens frondosa, Atriplex sagittata, and Impatiens glandulifera. In the recent past Atriplex oblongifolia and Xanthium albinum are disseminating. The spreading of the neophytes is discussed as well as the decrease of genuine species. The present paper is part of a larger designed investigation of the flora riverbanks of the Weser System. The dynamics of the flora along the upper part of the Weser can be followed on quantitative basis in future by the help of 42 sample areas. This underlies a long-term monitoring
