MILLER, JOSEPH T and RANDALL J BAYER.* Centre for Plant Biodiversity Research, GPO Box 1600, Canberra, ACT Australia. - Towards an understanding of the Mulga complex (Acacia aneura): polyploidy, hybridization and apomixis create dynamic population structures.
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