The distribution ofSaxifraga ferrugineaand the problem of refugia in northwestern North America

摘要

Saxifraga ferruginearanges over that part of northwestern North America which was glaciated in late Pleistocene time. A survey of chromosome numbers within the species places diploids south of the ice margin and, in a few locations, inside the margin. Elsewhere only polyploids have been found. The distribution of diploids and polyploids supports the reality of refugia on Kodiak Island and the Queen Charlotte Islands.It is proposed that polyploids evolved either before or during recession of the ice and that they rather than the diploids were the colonizers of the newly open disturbed terrain.