Acacia systematics and development of a model system for co-evolutionary studies

A project undertaken by the Centre for Plant Biodiversity Research and supervised by Joe Miller

Acacia is a diverse assemblage including over 950 species, most of which occur in Australia.  Acacia species frequently dominate undisturbed ecosystems providing the key component of plant communities by interacting with a broad range of organisms, including nitrogen fixing rhizobial bacteria, mycorrhizal fungi, disease-causing fungal rusts and herbivorous insects. Interactions among these organisms determine the health of the environment and acacias can provide a model system for investigating the ecological and co-evolutionary consequences of these interactions.  However, we currently lack a broad understanding of evolutionary relationships within Acacia, which would provide the foundation for this co-evolutionary research. Our long-term aim is to build a model research system that explicitly links the evolutionary dynamics of interacting organisms with the Acacia phylogeny.  This information will inform more applied work in weed biocontrol, plant revegetation programs as well as allowing us to address fundamental questions in ecology and evolutionary biology.

This Slade Foundation supported project focuses on developing a broad framework phylogeny of the Australian Acacias.  Our goal is to sample 90% of the species with a six gene phylogeny. The molecular phylogeny will be used in several ways.

  • Determine the evolutionary relationships of the Acacia species
  • Determine the timing of major evolutionary splits in Acacia.
  • Contribute to a phylogenetic classification of the genus.
  • Investigate cophyletic interactions with allied biota (thrips, beetles etc…)



With the data from our molecular systematics studies we can infer the changes in plant architecture, leaf form and biogeographic distribution of species over time.  We commonly represent these DNA sequence data as a “Phylogenetic Tree,” basically a branching diagram with closely related species connected by short branches and more distantly related species connected by long branches.

Beginning on Wattle Day 2010 (September 1, 2010),  we will exhibit a live plant display in the shape of the latest phylogenetic tree, “A Tree of Trees.”  Over 100 potted wattle species will displayed at the Australian National Botanic Gardens with the exhibition shaped into the form of the latest phylogenetic tree (Fig 3).  Groups of related wattles will be connected by branches (mulch paths), where the length of the branches indicates their relative evolutionary relationship.  Visitors examining this interactive display will be able to investigate plants that are closely related and compare them to plants that are more distantly related.  In particular the display will highlight the incredible changes in leaf form and sizes in the wattles.  The potted plants will be labeled with species information sheets and the display will contain information on the methodologies and goals of this biodiversity research. 


Figure1.  Some of the phyllode diversity of Acacia species.

Figure 2.  Acacia aneura.

Figure 3.  Cartoontree depicting the “Tree of Trees” exhibition to be held at the Australian National Botanic Gardens in Canberra, Sept-Oct 2010. The tree trunk and branches are mulched paths leading to leaf tips which contain potted Acacia species arranged by phylogenetic relationships.