Understanding the origins of the Australian flora by integrating molecular phylogenies and fossil data in the Proteaceae

A joint project between the Royal Botanic Gardens Melbourne (RBGM) and the Botanic Gardens and Domain Trust Sydney (BGDTS) jointly supervised by Prof David Cantrill (RBGM), and Dr Dan Murphy & Dr Peter Weston (BGDTS)

The Proteaceae are an iconic family of plants with a Gondwanan distribution. Within Australia Persoonia (Proteaceae) is diverse with approximately 100 species and high regional endemism. The monotypic genera Acidonia (SW Australia) Garnieria (New Caledonia) and Toronia (New Zealand) are either closely related to, or nested within, Persoonia. Our study will combine phylogenetic information, geographic patterns of taxa, and molecular dating to produce an area chronogram (which shows the sequence of differentiation of areas on a geological time scale) for Proteaceae subfamily Persoonioideae. This will enable us to test different historical biogeographic hypotheses. Firstly, the informal infrageneric classification of Persoonia suggests that the genus includes multiple groups showing east-west disjunctions. The molecular phylogeny will test this assertion and whether multiple east-west disjunctions are the result of a single historical event as recently suggested. These results can be compared more broadly with those for other genera with similar distributions, such as Banksia, which has been investigated in some detail already. We will be better able to understand the biogeographic history of regions of endemism within Australia, including the southwestern Australian biodiversity hotspot.

Australian vegetation is now dominated by a large, central arid zone that separates several marginal “islands” of more mesic biomes (including sclerophyll forests, sclerophyll woodlands and heathlands). The origins of this pattern remain controversial with two competing hypotheses. One postulates that this diversity was derived by repeated colonisation events from the mesic areas predicting repeated sister relationships between mesic and arid areas. The other holds that the arid vegetation evolved in situ as the Tertiary rainforests contracted and the continent dried out resulting in arid groups in a particular genus or family that are related as a single lineage. Persoonia (Proteaceae) is an ideal group to test these hypotheses as it is diverse with approximately 100 species and has high regional endemism: 42 species are confined to southwestern Western Australia, 41 of which occur in the SW Australia biodiversity hotspot, 54 taxa are found in eastern Australia, and one species occurs across northern Australia (Persoonia falcata). The distribution pattern of Persoonia is seen in many other larger Australian genera (e.g. Banksia-Dryandra, Hakea, Grevillea). Although some of these genera extend further into the arid zone, targeting a group with multiple arid-mesic relationships will best test our invasion versus in situ origins hypotheses. Similar distributions and patterns of diversity may be the result of similar processes, and by studying a tractable group, in terms of species numbers, we will be better able to understand current diversity patterns in other distinctive elements of the Australian flora. An area chronogram will be produced, allowing us to test hypotheses of the pattern and timing of fragmentation of the mesic and arid biomes of Australia. This information will contribute to our understanding of Australia’s largest biome, the arid zone, and will contribute to understanding the evolutionary response of organisms to aridity, a particularly pertinent finding now, as climate change impacts on Australia. 

Figure 1. Persoonia tropica

Figure 2. Persoonia chapmaniana

Figure 3. Garnieria spathulifolia