title: Phylogenetic relationships of Betula species (Betulaceae) based on nuclear ADH and chloroplast matK sequences.
abstract: The phylogenetic relationships within the genus Betula (Betulaceae) were investigated using a part of the nuclear ADH gene and DNA sequences of the chloroplast matK gene with parts of its flanking regions. Two well-supported phylogenetic groups could be identified in the chloroplast DNA sequence: one containing the three American species B. lenta, B. alleghaniensis, and B. papyrifera and the other including all the other species studied. The ADH gene displayed more variation, and three main groups could be identified. In disagreement with the classical division of the genus Betula, B. schmidtii and B. nana grouped with the species in subgenus Betula, and B. ermanii grouped with species in subgenus Chamaebetula, including B. humilis and B. fruticosa. The ADH phylogeny suggests that several independent polyploidizations within the genus Betula could have taken place. The ADH and chloroplast phylogenies were in part incongruent due to the placement of B. papyrifera. The most likely reason for this seems to be cytoplasmic introgression.
authors.affiliation: Department of Biology, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland;
authors.forename: Pia
authors.initials: P
authors.lastname: Järvinen
authors.forename: Anna
authors.initials: A
authors.lastname: Palmé
authors.forename: Luis
authors.initials: L
authors.lastname: Orlando Morales
authors.forename: Mika
authors.initials: M
authors.lastname: Lännenpää
authors.forename: Markku
authors.initials: M
authors.lastname: Keinänen
authors.forename: Tuomas
authors.initials: T
authors.lastname: Sopanen
authors.forename: Martin
authors.initials: M
authors.lastname: Lascoux