A TAXONOMIC STUDY OF WESTERN CANADIAN SPECIES IN THE GENUS BETULA

Abstract

Five western North American birches, Betula fontinalis, B. glandulosa, B. glandulifera, B. resinifera, and B. papyrifera, are studied taxonomically. Four hybrids, B. × winteri, B. × sargentii, B. × arbuscula, and B. × uliginosa, are described for the first time and three others, B. × utahensis, B. × eastwoodae, and B. × sandbergii, are also included. Populations formed when species are in contact have been analyzed and the nature of several hybrid entities determined. B. × uliginosa results from B. resinifera × B. glandulifera. In this population, introgression is toward B. glandulifera, which has the higher chromosome number. B. glandulifera also hybridizes with B. glandulosa producing B. × sargentii. Most gene flow is toward B. glandulifera, which has the higher chromosome number. In B. glandulosa × B. fontinalis (B. × eastwoodae) introgression was little influenced by environmental selection, the hybrid was as common as either parental species, and any gene flow was in either direction. B. × utahensis results from B. papyrifera × B. fontinalis. Introgression is toward B. papyrifera. Hybridization of B. × sargentii and B. papyrifera produces B. × arbuscula, a rare hybrid. Hybridization of B. resinifera and B. papyrifera results in B. × winteri, with introgression in both directions. B. × sandbergii results from B. papyrifera × B. glandulifera. Probably as a result of environmental influence in the analysis area, introgression was toward B. glandulifera, with the lower chromosome number.