Molecular data are becoming easier to collect and can help us address many important questions in invasion biology. However, for most organisms, the connection between molecular loci and phenotypic traits is not direct. Here, I review some fundamentals of population and ecological genetics and point out limitations of molecular data, particularly when the data are from loci without a known connection to the phenotype. I then discuss the ways that molecular data may facilitate management of invasive weeds, despite the limitations. Key uses of molecular data in invasive weed management include identifying species, determining their origins, and understanding mechanisms and rates of spread.

Additional index words: Biological invasions, ecological genetics, phylogeography.

Abbreviations: AFLP, amplified fragment length polymorphisms; cpDNA, chloroplast DNA; RFLP, restriction fragment length polymorphisms.