Gastrolobium (Fabaceae: Mirbelieae) is a genus of legumes that is endemic throughout southwest Western Australia. This genus is important economically, as it produces Sodium monofluoroacetate (a.k.a. 1080) and is of particular interest to farmers, as many deaths to sheep and cattle have been attributed to it in the past. There has been controversy over the generic delimitation of Gastrolobium, particularly in regard to the closely related genera Brachysema, Jansonia, Nemcia, and Oxylobium. Some morphological variation exists between the genera, but none of them can be readily separated by reliable characters, but rather by a suite of characters that overlap significantly between genera. Also, presence of 1080 was used as a secondary character to separate Gastrolobium and Nemcia, but fluoroacetate has been found in some species of Nemcia. Current studies using molecular tools (using the psbA-trnH intergenic spacer and the trnK 5 intron from chloroplast DNA and ETS from ribosomal nuclear DNA) have shown these genera to be very paraphyletic. Gastrolobium includes not only Nemcia, but also Jansonia and Brachysema, and one species of Oxylobium, O. lineare. The phylogenetic relationships revealed in this study within Gastrolobium sensu lato will lead to a recircumscription of genera in this complex, and lead to the reevaluation of evolutionary traits in this group, particularly fluoroacetate.

Key words: external transcribed spacer, Fabaceae, fluoroacetate, Gastrolobium, matK, molecular phylogeny