Molecular systematics of subtribe Banksiinae (Banksia and Dryandra; Proteaceae) Based on cpDNA and nrDNA sequence data: Implications for taxonomy and biogeography

Abstract

Despite considerable research interest in the subtribe Banksiinae (Banksia L.f. and Dryandra R.Br.), no strongly supported phylogenetic hypothesis for the relationship between the genera exists, nor have molecular characters been sampled for phylogenetic reconstruction at any level. In this study, DNA sequence characters were sampled from chloroplast DNA (cpDNA; the trnL intron, the trnL 3′ exon, and the spacer between the trnL 3′ exon and trnF) and nuclear ribosomal DNA (nrDNA; both internal transcribed spacers) of 18 species of Banksia and five of Dryandra, with six outgroup taxa from the subfamily Grevilleoideae. The molecular characters provided the opportunity to code taxa outside of Banksia for cladistic comparison with the genus—an opportunity not previously provided by morphological characters. Cladistic analyses, using parsimony, explored the effects of various weightings of transition to transversion events and base substitution to insertion and deletion events to determine which relationships in the cladograms were robust. The trnL/trnF and ITS characters strongly supported a paraphyletic Banksia with respect to a monophyletic Dryandra. The molecular results supported a single root for Thiele and Ladiges’(1996) unrooted morphological cladogram along the branch between the Isotylis to B. fuscolutea clade and the Grandes to B. tricuspis clade. George’s (1981) subgenus Banksia and section Banksia appeared dramatically non-monophyletic. The distribution of eastern taxa at derived positions on the molecular cladograms suggested considerable cladogenesis in the the genus prior to the formation of the Nullarbor Plain during the Tertiary.