Central Western Norway was divided up into seven mountain areas, representing an east‐west gradient from Hardangervidda (area A) westwards to the islands of Tysnes and Stord (area G). The alpine flora of totally 138 species thins out gradually where A has the greatest number (137 species) and G has the fewest (55 species). A drop of 83 species from east to west must be due to ecological barriers which prevent growth on the coastal mountains. Several factors have been taken into account and discussed. Rich Cambro‐Ordovician rocks are present in all the explored areas, but the zone narrows towards the west due to the overlying base‐poor thrusted rocks in the Caledonian nappe system. West of Hardangervidda, the summits of the mountains are almost entirely composed of acid rocks, and habitats for basiphilous species are therefore not present at the highest altitudes. Climate during the season of winter dormancy differs much more than during the growing season between east and west. Alpine plants require climatic conditions conducive to the termination of growth in autumn, a state of quiescence due to cold winters, and stable snow conditions which give a rapid transition from winter to summer. As the oceanic climate does not comply with these requirements, the number of alpine species declines. The alpine flora of Westem Norway is closely related to that of Great Britain. This is probably explained historically by a common origin during the Late Weichselian p