The weed monitoring in France (′Biovigilance Flore’) conducted between 2003 and 2005 was used in order to compare the oilseed rape (Brassica napus L.) weed flora with a former weed survey realized in the middle of the 1970’s. Using the kind and the degree of specialization of the weed species, this study shows that multiple selective processes operate at various temporal scales, ranging from the crop (one year), to the rotation (about three years) and to decades. Compared to the 1970’s, there are more generalist weed species in oilseed rape crops nowadays. In the same time, the number of weed species highly adapted to oilseed rape has increased. About 30 % of the increasing species have been selected by one or several cultivation methods used in oilseed rape culture. But the homogenization of the weed flora could be due to (1) the extension of some rotations including summer crops (maize, sunflower) which could favour the species able to rebuild their soil seed bank every year and (2) the standardization of environmental cropping conditions which could threaten the species highly adapted to particular environments (temporarily waterlogged soils). On a national scale, the soil and the climate are the most effective factors acting on weed species composition. They make the oilseed rape weed flora of the West plains stand out from the flora of the North-East limestone plateau. The effect of interaction between crop rotation and environmental conditions is discussed.