This piece of work describes the consequences of climatic oscillations during the Pleistocene and the last glacial maximum (LGM) on the genetic relationship within four plant species co-distributed along the European Mediterranean and Atlantic coasts. The four species occur in different habitats, taxonomicaly unrelated, but they share means of seed dispersal and history. Molecular polymorphism in three of the species (Salsola kali, Halimione portulacoides and Crithmum mritimum) indicated a clear Mediterranean - Atlantic subdivision. In the three species, the time of seed buoyancy ranges from one to four weeks. In the fourth species (Calystegia soldanella), no geographical clustering of genetic data was revealed. Seeds of this species could float in sea water for several years and resulted in long distance dispersal.