Genetic composition and morphological variation among populations of the invasive grass, Phalaris arundinacea

Species that become invasive after being introduced into a new range often experience genetic bottlenecks and strong selection to adapt to their new environment. We looked for evidence of such processes in unmanaged populations of invasive reed canary grass (Phalaris arundinacea L.). This grass species is planted as a forage crop in North America but has also invaded wetland areas. We compared isozyme variation in pasture and wetland populations of this species. We did not find any indication of a genetic bottleneck: wetland populations comprised as much diversity as pasture populations and both had as much diversity as the two cultivated varieties of reed canary grass that we sampled. We also cultivated plants from wetland and pasture populations and estimated genetic variance for several morphological traits. We did not find any significant differentiation to suggest differential selection between populations from the two habitats. In fact, we found the highest amount of genetic diversity, both isozymic and quantitative, within populations. We also found strong evidence that reed canary grass reproduces primarily clonally. The implications of these observations in terms of the origin of invasive populations of reed canary grass are discussed.Key words: invasive species, Phalaris arundinacea, reed canary grass.