Phylogenetic relationships in Abies (Pinaceae): evidence from PCR-RFLP of the nuclear ribosomal DNA internal transcribed spacer region

Abstract

Phylogenetic analysis of restriction site data from the nuclear ribosomal DNA internal transcribed spacer region (ITS) was conducted for Abies to evaluate different infrageneric classification schemes. Twenty-eight species representing major morphological subgroups of the genus were included in this study. Thirty-three unambiguous restriction sites were scored from nine enzymes. The data were analysed using parsimony and neighbour-joining methods to infer phylogenetic relationships within the genus. Seven subclades that more or less correspond to previously recognized subgroups were resolved from these analyses: (1) sect. Bracteata, (2) sect. Balsamea (excluding A. kawakamii), (3) sect. Amabilis, (4) an eastern Asian group including sect. Momi, part of sect. Pseudopicea, and A. kawakamii, (5) core of sect. Pseudopicea, (6) a Mediterranean–south-western Asian group containing sect. Abies and sect. Piceaster and (7) sect. Nobilis. Lineages (4) and (5) are likely to be sisters, which are, in turn, sister to lineage (6). The results also suggest that this large Eurasian clade is most closely related to subclade (2) and the monotypic sect. Bracteata is most closely related to sect. Balsamea, but these relationships are supported by bootstrap values of less than 50%. These results indicate that the eastern Asian – North American disjunct section, sect. Balsamea, is monophyletic (96%) when A. kawakamii from Taiwan is excluded; species of sect. Abies and sect. Piceaster (Mediterranean and south-west Asia) are closely related, but the monophyly of each section remains unclear. The results also suggest that sect. Pseudopicea is not monophyletic; species from eastern China and the Qingling Mountains of this section appear to be more closely related to sect. Momi and A. kawakamii than to the other species of the same section. Species of sect. Grandis separate from the remaining species of Abies by having an approximately 500 base pairs longer ITS region. This study provides the first molecular-based phylogenetic hypothesis of Abies to be tested with additional data and broader sampling.