Macrozamia, a genus of cycad found only in Australia, is now believed to have arrived inland far more recently than initially thought.
The MacDonnell Ranges cycad, Macrozamia macdonnellii, in Cycad Gorge, Finke Gorge National Park, Northern Territory, Australia (User:Cgoodwin / Wikipedia.org / CC BY 3.0)
Considered to be the world’s oldest living plants, cycads are a group of non-flowering plants that look like palms but reproduce with cones and have existed as a group since about 270 million years ago.
Researchers led by the University of Queensland (UQ) have found that the MacDonnell Ranges cycad, Macrozamia macdonellii, is too similar to its relatives more than 1200 km away in eastern and coastal Australia to have been isolated in central Australia for 30 million years.
“Comparisons between the plants revealed little difference,” said James Ingham, a PhD candidate at UQ and lead author of the paper published in the journal Diversity and Distributions. “Some of the central Australian plants have chloroplast DNA with an identical sequence to those in eastern Australia.”
“This is much too similar for the plants to have been isolated in central Australia since the Eocene period, instead suggesting that Macrozamia in central Australia has only become isolated sometime in the past couple million years.”
“In contrast, plants from Western Australia have been isolated from plants in eastern Australia for much longer, possibly for as long as ten million years or more.”
Macrozamia cycads occur in south-west Western Australia, central Australia and along the east coast, including Queensland and New South Wales, but nowhere in between those three regions.
The MacDonnell Ranges cycad is a species unique to central Australia and is the only cycad in the region.
“Until now, researchers have generally believed that the MacDonnell Ranges cycad has survived in central Australia since the Eocene period, more than 30 million years ago when Australia’s climate was much wetter and rainforest much more widespread,” Ingham said.
Because cycad fossils from the Jurassic period look very similar to cycads living today, it was previously assumed that cycads have remained more or less unchanged for millions of years.
Overall, the study supports two other recent studies indicating that living cycad groups have been around for only the past 10-20 million years, much younger than during the Jurassic when cycads served as dinosaur food.
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Bibliographic information: Ingham et al. 2012. Ancient relicts or recent dispersal: how long have cycads been in central Australia? Diversity and Distributions, article first published online 26 June 2012; doi: 10.1111/j.1472-4642.2012.00936.x
