Weeds growing in cultivated areas are usually characterized as having high phenotype plasticity and genetic adaptability. They are frequently well-adapted to disturbance and often seed prolifically (Adahl et al., 2006). Thus, improving the current knowledge on the genetic diversity of weed populations is a challenge for management, primarily because this variability may be an important tool in determining the adoption and efficiency of weed control methods. Genetic markers may be important to improve current knowledge about important aspects of weeds, and may provide needed information to understand patterns of weed invasion, heritability of traits (e.g. herbicide resistance), taxonomic relationships, point of origin, and gene flow. Studies on genetic diversity both at population and species levels are important for weed management, and represent a source of information about genetic bottleneck effects, fitness, and the number of input events that contributed to a successful introduction (Goolsby et al., 2006; Hufbauer, 2004; Sterling et al., 2004). Improving the knowledge about genetics of weeds can provide vital information for the development of innovative control options (Slotta, 2008).