Frangula alnus (Alder Buckthorn, also known in North America as Glossy buckthorn) is an ornamental woody species invading North American forests and prairies. De Kort et al. propose that repeated introductions from European source populations into North American parks facilitated the invasion of natural areas through providing stable and genetically diverse park populations.
Using annotated genetic markers (SNPs), they show that multiple introductions from a limited number of European port regions to American parks led to the establishment of bridgehead populations with high allelic richness, allowing for continuous secondary migration to natural areas as well as rapid allele frequency shifts at putatively adaptive SNPs.
Hanne De Kort, Joachim Mergeay, Hans Jacquemyn, Olivier Honnay, 2016, 'Transatlantic invasion routes and adaptive potential in North American populations of the invasive glossy buckthorn, Frangula alnus', Annals of Botany, vol. 118, no. 6, pp. 1089-1099 http://dx.doi.org/10.1093/aob/mcw157