Acacia aneura, also known as mulga, is the core species of the mulga complex, a widespread group that is dominant in much of arid Australia. Acacia aneura and the 10-15 other species that comprise the complex are taxonomically difficult, due to the morphological variability that occurs within populations, over its entire range and within A. aneura itself. These species vary in phyllode, fruit and seed characters, as well as flowering time and growth habit. It is not unusual to find five or six obviously different forms, with or without intermediates, growing side by side in a population. This complexity has made taxonomic treatments of the group difficult. This study utilizes morphology, cytogenetics and microsatellites on material collected throughout the range of mulga. Results indicate the morphological variation is being caused by periodic hybridization among morphotypes buffered by the effects of polyploidy and is being maintained by apomictic seed production. From field work it appears that the retention of juvenile characters, such as plant architecture and phyllode morphology is also complicating our understanding of the complex. These new data have given an insight into the population structure and overall variation within mulga. In addition these results shed light into the on evolutionary mechanism affecting the Australian arid-zone flora.

Key words: Acacia, apomixis, arid-zone evolution, Fabaceae, hybridization, polyploidy