INTROGRESSIVE HYBRIDIZATION BETWEEN BETULA NANA L. AND B. PUBESCENS EHRH. IN NORTH‐WEST ICELAND

Abstract

In Iceland the genus Betula is represented by B. nana L., which has little morphological variation, and a variable series of shrub and tree birches. A comparison of these variable populations in the Skjaldfannardalur area, Isafjardardjup, north‐west Iceland with British populations of B. pubescens Ehrh. (2n= 56) and B. nana (2n= 28) using histograms of hybrid indices has been made and it is concluded that the variation is due to introgressive hybridization between B. pubescens and B. nana. The introgressed B. pubescens populations have a lower fertility than those of B. nana. The mechanism of gene flow is discussed and it is suggested that it is more likely to be either direct from diploid to tetraploid levels or via intermediate triploids rather than through the formation of aneuploid complexes. Copyright © 1968, Wiley Blackwell. All rights reserved