The work analyzes the importance of plant diversity in agroecosystems and the effects of the intensification of agricultural and landscape practices on plant diversity. The review of several studies carried out by the research team highlights that agricultural intensification, both at the field and landscape levels, negatively affects the abundance and specific richness of the flora. The comparison of the arvense flora of the mediterranean dryland cereal crops between the 50s and the present reflects the reduction of the arvense flora, especially the flora of the harvests and the decrease of the abundance of functional groups such as legumes and entomophilous plants. The effect of agricultural practices and the complexity of the landscape varies depending on the flora studied. Thus, the complexity of the landscape is the main factor that affects the configuration of the vegetation of the margins, while the intensity of the agricultural practices is the main factor to explain the differences in the arvense flora in the center of the fields. Finally, the article analyzes various proposals for the management of agrosystems with the objective of reconciling agricultural production and biodiversity conservation in the Mediterranean region.