Orchids have minute seeds and can disperse over long distances. Hedrén et al. use genetic markers to track how the marsh orchid Dactylorhiza majalis ssp. lapponica (Orchidaceae) colonised the Baltic Sea island of Gotland repeatedly (and mostly from the east) after the last ice age.
These multiple colonization events have resulted in a mosaic pattern of genetic variation, such that adjacent populations are not necessarily closely related. Hedrénet al. also find that the genetically most diverse populations are located at older sites, suggesting that genetic diversity builds up over time.
