A molecular phylogeny of the endemic Australian genus Gastrolobium (Fabaceae: Mirbelieae) and allied genera using chloroplast and nuclear markers

Abstract

Gastrolobium (Fabaceae: Mirbelieae) is an endemic Australian genus that produces toxic sodium monofluoroacetate. A phylogenetic reconstruction of Gastrolobium and the related genera Brachysema, Callistachys, Jansonia, Nemcia, Oxylobium, and Podolobium is presented, using sequence data from three regions-the psbA-trnH intergenic spacer and the trnK 5' intron from chloroplast DNA and the 3' end of the external transcribed spacer (ETS) from nuclear ribosomal DNA. Gastrolobium is shown to be paraphyletic, with Brachysema, Jansonia, Nemcia, and Oxylobium lineare nesting within it, and Nemcia is shown to be polyphyletic within Gastrolobium. Past key morphological characters, such as fluoroacetate content and characters associated with pollination syndrome, are shown to be homoplastic, with fluoroacetate possibly a plesiomorphic condition lost in more derived species. Podolobium is also shown to be polyphyletic, with the P. ilicifolium group sister to Gastrolobium and the P. alpestre group sister to Callistachys, a member of the Oxylobium group. It is recommended that Gastrolobium be expanded to include Brachysema, Jansonia, Nemcia, and Oxylobium lineare, while further work is required to test the sister-group relationship between Podolobium s.s. (sensu stricto) and Gastrolobium.