392 relevés of arable land in central and northern Germany were resampled after 50 years, with the aim to quantify impacts of agricultural intensification on arable plant vegetation. Today, most arable plant communities consist of only a few highly stress-tolerant generalist species while most specialist taxa have disappeared. The regional species pools have decreased on average by 23 % since the 1950/60s, the median plot-level species richness in field interiors declined even by 71 %. A rough extrapolation suggests that the population size of many formerly characteristic arable plant species has decreased by up to 95-99 % over the past 50 years. Population genetic analyses show that the genetic structure is generally detrimental, and the genetic diversity of extant populations is lower in highly endangered species than in less threatened taxa. The national target to halt biodiversity loss in agricultural ecosystems by 2015 will not be reached. Innovative approaches to conserve the last remaining populations of the formerly rich arable plant flora are thus urgently needed.