Our Gondwanan gum trees
OUR EUCALYPTS HAVE a more amazing past than anyone ever guessed. Their oldest fossils have been found on the other side of the world – in South America. Beautifully preserved gum nuts, blossoms and leaves have been unearthed in Patagonia, dating back an incredible 52 million years. At that time Australia, Antarctica and South America were still joined as part of Gondwana. Antarctica was so warm it probably had gum trees on its hillsides, waving down at giant penguins in the water.
In stories of Australia’s past, much is made of its Gondwanan legacy, of plants such as southern beeches (Nothofagus species) that disclose old connections by growing in Australia and South America. The plants dubbed Gondwanan are usually rainforest trees, fitting our picture of the past as lush and steamy.
Red flowering gum (Corymbia ficifolia) photographed in Sydney, NSW. (Image: OzinOH / Flickr)
The Patagonian fossils establish eucalypts as Gondwanan plants. New Zealand had them as well, along with banksias and she-oaks. Eucalypt remains have allegedly been found in China, India, Europe and North America, but all these identifications are dubious and probably wrong.
South America became part of the Eucalyptus story because it has vast sedimentary layers subject to intense searches. An even older fossil, found in southern Queensland, may show eucalypt gum nuts, but we can’t be certain. Eucalypts aren’t as good as rainforest trees at leaving fossils behind, because they don’t grow as often in wet places suiting preservation. With all their closest relatives in and around Australia we can be sure they started out here rather than South America.
They went traveling at a time when many exchanges were going on. Marsupials entered Australia from Antarctica, while parrots went the other way. A jaw found in South America shows that platypuses were among the travellers, although which way they went is unclear.
Eucalypts are often thought of as a young group that took over Australia after it drifted north to become drier with more fire. But there are more than 800 species here, and while many are no doubt young, the sheer number of them, and all the variation, fits an ancient origin.
The Patagonian fossils look completely modern, which means that some of our eucalypts have not changed materially for more than 50 million years. Some experts believe they overlapped in time with dinosaurs. They are one reason to doubt the old idea that Australia’s woodland and heathland plants are much younger than her rainforest plants. We should revere them as a modern Australian success story with a spectacular past.
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