Native and alien invasive plants: More of the same?

We compare the ecological and habitat characteristics of alien and native vascular plants which have recently expanded in range in England, Scotland, the Republic of Ireland and the Netherlands. In the great majority of respects, expanding aliens and natives are functionally indistinguishable. However, there are a few consistent differences: aliens are more likely than natives to be clonal, polycarpic perennials with erect, leafy stems, and to have transient seed banks. We discuss these trends in the context of the difficulties faced by aliens in invading mostly closed plant communities in relatively cool, damp climates. Our results are consistent with some predictions of the attributes of 'ideal' invaders, but contradict others. We argue that the ecological attributes of successful alien invaders are strongly habitat-dependent.