AbstractAnthoxanthum alpinum has a continuous distribution from the treeline (1700 m) to the summit ridges (2830 m) in Arpette and Belalp of Valais , Swiss Alps. The highest and lowest sites of the transect differ by almost 1000 m in elevation , but only an average of 1. 4 km apart . A significant clinal variation was observed at three allozyme loci ( P_x- 1 , G_ot- 2 and M_dh- 1) on all three transects. It suggests that gene flow among sub-populations may be too weak to overcome the effects of natural selection in favor of adaptations to local conditions , and that temperature variables may function as major selective force in this case.