Leaf-shape as an indicator of introgression between<i>Betula pendula</i>and<i>B. pubescens</i>

Abstract

Summary Leaf-shape comparisons were made between individual trees in a mixed wood containing B. pendula and B. pubescens, and two relatively pure stands. Data sets were subjected to analysis of variance, principal components and discriminant analyses in order to study within-tree variation, variation within each species and the relationships between them. Within-tree variation was found to be much less than that between trees and principal component analysis provided a separation of the material into species groups and indicated extensive variation within them. The employment of a discriminant function sharpened the separation of the pure woods and pointed to the occurrence of possible hybrids and back-crossed individuals within the mixed wood. The findings indicate that gene flow probably proceeds from the diploid to the tetraploid level.