Botanic Gardens Trust, Sydney, Australia

Lauraceae

A molecular phylogeny of the Australian Lauraceae reveals encouraging patterns of speciation along a background of aridification

Dr Marlien van der Merwe - Scientific Officer
Dr Maurizio Rossetto - Manager Evolutionary Ecology
Dr Peter Weston - Senior Principal Research Scientist
Dr Darren Crayn - Australian Tropical Herbarium

The family Lauraceae is an excellent group to use as a model to investigate patterns of species divergence within the Australian rainforest. The fossil flora of Australia indicates that the Lauraceae has been a part of the Australian Flora for as long as rainforest has been a prominent vegetation type in Australia. In addition the distribution of the woody Lauraceae mirrors the distribution of rainforest along the east coast and many species exhibit interesting disjunct distributions between the tropics and the subtropics of far north Queensland and Northern NSW. The majority of Australian laurel species are either restricted to the tropics or the sub tropics. In Australia 30 species of Cryptocarya are found in the tropics, 13 in the sub-tropics and 4 species have a distribution that overlaps the two regions. Amongst the species in the two genera Endiandra and Beilschmiedia 32 species occur in the Tropics, 11 in the sub-tropics and 5 in both regions.

A successful ABRS grant of Maurizio Rossetto, Darren Crayn and Peter Weston enabled us to build a species level phylogeny of the Australian woody Lauraceae and use this phylogeny to explore patterns of diversification within the group. Field work was conducted in far north Queensland with the help of Bruce Gray (ATH, Cairns) and Andrew Ford (CSIRO, Atherton) and Rob Kooyman (Mullimbimby). We obtained sequence data for 2 cpDNA regions (PsbA-TrnH and the trnL-trnF) and one nuclear region (partial RPBii) for over 94% of the woody Australian species.

The phylogenetic analysis indicate that the Australian Cryptocarya are a well supported monophyletic clade but  Endiandra and Beilschmiedia are polyphyletic. The taxonomy of these two groups will have to be revisited. 

We used fossil and secondary calibrations to infer estimated times since well supported molecular clades shared a common ancestor. To our surprise the preliminary results from the molecular dating indicate that more than 50% of the Cryptocarya species diverged within the last 15 million years. Thirty percent of the species in the Endiandra/Beilschmiedia show a similar pattern of recent speciation. These patterns of recent speciation in the Australian Lauraceae may indicate to us that since the onset of aridification on the Australian continent 15 million years ago rainforest diversified in species numbers with the majority of species the product of vicariance. One of the products of aridification is the current island like archipelago of rainforests along the east coast. The fragmentation of a once more continuous rainforest facilitated isolation of populations and this likely caused the increase in the rate of speciation as found in the Lauraceae. While many of the young species show a very disjunct distribution with two sister taxa occurring only in the two centres of rainforest diversity (the Australian wet tropics and the sub-tropics of northern NSW) others such as the group containing, Cryptocarya onoprienkoana, C. rigida, C. rhodosperma and C. erythroxlyon occur across the entire distribution of the rainforest along the east coast. This wide distribution of close relatives may indicate to us that since the divergence the species responded to favourable climatic periods and expanded across the available habitat. In addition to our findings that many of the extant Australian laurel species are relatively young our results also indicate that the Cryptocaryeae group is most likely of Gondwanan origin. However, further research and samples from outside Australia is needed to clarify this issue. 

 

 

 

 

Bruce Gray and Andrew Ford collecting laurels
Bruce Gray and Andrew Ford collecting laurels in far north Queensland. Photo: Marlien van der Merwe
distribution and phylogenetic relationships

The distribution and phylogenetic relationships of five Australian Lauraceae species. The closest relative to these 5 species in our phylogenetic analysis was found to be Cryptocary alba, a species from South America.