Botanic Gardens Trust, Sydney, Australia

Cycad evolution and diversity

Dr Nathalie Nagalingum - Systematic Botanist

Cycads have captured wide interest as survivors and relicts from the age of dinosaurs. However, my research shows that although the lineage is ancient, the living cycad species are all strikingly young. I used fossil-calibrated molecular phylogenies with representatives of two-thirds of all living species from across the geographic distribution of cycads. The results indicate that the species began to diversify recently, only ~12 million years ago and ~55 million years after the extinction of the dinosaurs. There were parallel radiations within multiple genera, and these were nearly synchronous and were global. Just as remarkably, they ceased to diversify. The findings suggest that cycads likely responded to a change in global climate occurring 12 million years ago.

This research gained broad public appeal and attracted media interest at ABC 702 AM Breakfast with Adam Spencer, ABC 702 AM Mornings with Deborah Cameron, ABC nightly national television news, ABC Science Online, COSMOS magazine and the Sydney Morning Herald and many others.

My research on cycads is continuing through several projects addressing species-subspecies-hybrid boundaries, population genetics, phylogeny, genomics, physiology and biogeography. One particular focus is the complexes of species-subspecies-hybrids of the genus Cycas occurring in Queensland and in the Northern Territory. DNA data will provide an objective way to assess these entities and it will be used subsequently to revise morphological taxon boundaries. Ultimately, this work will inform decisions on which populations are most critical for conserving and address the question of how many species of cycads are in Australia. 





Macrozamia johnsonii leaf. Plant growing in the Royal Botanic Garden, Sydney.

The pollen cone and leaves of Cycas thouarsii. Plant growing in the Royal Botanic Garden, Sydney. 

A pollen cone borne on the species Cycas taitungensis. Plant growing in the Royal Botanic Garden, Sydney.

Photos: Nathalie Nagalingum