Invasiveness of Oenothera congeners in Europe related to seed characteristics

genus Oenothera represents one of a few genera alien to Central Europe comprising a set of species differing in their invasive success, from successful invasion to rare. This study tests the hypothesis that higher seed production, smaller seeds and higher germination rates contribute to invasive potential within the genus Oenothera. The study tries to find relations between these species characteristics and their invasive potential and invasion history on a European scale. Measurements and experiments were performed on 15 taxa of this genus representing species of North American origin as well as hybrid taxa which probably originated outside their native range, some of which are invasive. Germination characteristics appear to be more important than pure seed quantity or its weight. In our study, preference for germination in the light was the only sig- nificant predictor of invasiveness. Species, which tend to germinate easily in the light, are best invaders.