Testing species delimitation in Acacia: are gidgee (A. cambagei) and Georgina gidgee (A. georginae) two distinct species?

Barbara Azevedo de Oliveira (The University of Queensland); Rod Fensham (The University of Queensland, Queensland Herbarium); Lyn Cook (The University of Queensland).

Acacia cambagei R.T. Baker and A. georginae Bailey are dominant woody species found in the Australian arid zone, spanning from Queensland to the Northern Territory and into the north of South Australia. These species, commonly known as gidgee, gidyea or gidgea, have significant cultural value in indigenous communities. Acacia georginae is valued for its edible resin, while A. cambagei is renowned for its durable timber, fuelwood and soil stabilisation. Distinguishing between A. georginae and A. cambagei remains challenging because, although existing keys rely on differences in pod and seed shapes, there is actually a continuum in the field. Keys state that A. cambagei has thin, straight pods with small oval seeds, whereas A. georginae is listed as having curved pods with large circular seeds. Acacia georginae is toxic and can be lethal to livestock, although there is variation in toxicity among individuals. Applying the Biological Species Concept, we use Angiosperm 353 sequence data to assess gene flow between and among populations of both taxa in sympatry and allopatry. Initial morphological analysis of herbarium material has confirmed a continuum of pod and seed characteristics across their distributions. Clarifying the taxonomic status of A. georginae and A. cambagei will contribute to managing and conserving these valuable woody species.