XVI International Botanical Congess

The dominant weed species invading maize and wheat crops in areas with particular soils of the Pampas for the last 60 years have been identified by phytosociological studies. Convergence among species of any trait having a selective advantage in the cropping environment should be expected. We found no evidence of such convergence when we investigated seed bank persistence, dormancy and germination characteristics of model species: Datura ferox, Avena fatua, Echinochloa cruss-galli, Tagetes minuta, and Galinsoga parviflora. The first species has a persistent seed bank, and sophisticated mechanisms of dormancy relief and termination, which have been related to environmental sensing. These traits gradually loose importance as we follow the above species list. However changes in these traits have been recorded when E. cuss-galli and A. fatua are subjected to different agricultural systems, suggesting an adaptive value for the invasion of human disturbed habitats.