Cytology ofBetula albaL. complex

Abstract

SynopsisThe morphological variation between and within species ofBetulahas resulted in taxonomic confusion which chromosome studies have been aimed at reducing. The paper briefly reviews the general situation and summarizes recent work at Aberdeen.Betulaforms a polyploid series with chromosome numbers ranging from 2n = 28 to 2n = 84. The native British arborescent birchesB. pendulaandB. pubescensEhrh. have respectively 2n = 28 and 2n = 56 chromosomes. Meiosis is essentially regular but many phenomena occur which may account for the production of gametes with non-haploid chromosome numbers. Variation in somatic chromosome number within the leaf tissues of both species is common and trees have been identified whose modal chromosome counts lie between 28 and 56. Some of these trees are of hybrid origin while others may aneuploidB. pubescens. The former types are sterile while the latter cross freely amongst themselves and with 2n = 28 and 2n=56 trees.