The Noordoostpolder is one of the polders in the former Zuiderzee, reclaimed in 1941 and 1942. A natural vegetation developed but was destroyed when the land was cultivated. Many adventitious species came into the area together with road construction materials and crop seeds. Nowadays these species have mostly disappeared, only a small number are still present. The polder consists of an area with sandy clay, bordered by an area with loam, sand and peat Calcareous sands are predominant here. It is shown that floristically this border area is quite different from the area with sandy clay, but also from the bordering part of the ‘old land’. 133 species characterize this border area. Many of these species show links with a number of different plant geographical districts. It is concluded that the border area deserves a plant geographical status of its own. In addition it is shown that in the former Zuiderzee-island Schokland the number of species has much decreased. In Urk the number of species increased slightly, but a number of species disappeared and others moved in.