Characteristic of segetal communities of order Centauretalia cyani, occurring in the administrative borders of Siedlce is presented in the paper. Presence of 2 associations and 4 communities, differentiated internally into: 2 subassociations, 8 variants and 3 subvariants. Totally 15 phytocoenoses of the lowest units were distinguished. The largest areas of the city cultivations were occupied by communities without characteristic species for described segetal associations, as: incomplete community of all. Aperion spicae-venti. Plots of association Vicietum tetraspermae were also frequent in the studied area. Presence of floristically rich plots of Papaveretum argemones – association of cereal weeds rarer and rarer noted in Poland is especially noteworthy. Segetal vegetation of Siedlce city is characterized by its floristic abundance and large participation of ruderal species passing from adjacent areas to arable lands.

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