Fossilised fruit scratches at the mystery of screw palms

Plants from the Pandanus genus grow in the tropics all over the world, where hundreds of different species are present. In Australia, there are 15 different Pandanus species, including the screw palm (which, of course, is not a palm).

But the plants’ history isn’t very clear – it’s not even obvious which continent Pandanus evolved on.

Now, thanks to the discovery in Central Queensland of a 30-million-year-old fossilised fruit, it seems the answer might be the prehistoric great southern landmass of Gondwana.

The fruit fossil was found in 2014 by Joe Bridgeman, on his property at Capella, roughly 50km north of Emerald.

After analysis by researchers from the Queensland Museum, the University of New England, the University of Queensland, and Kew Gardens in the UK, it’s been decided that it’s a Pandanus – and a new species at that.

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Man holding large green fruit bigger than his head in one hand, tiny brown rock smaller than his thumb in other hand
Dr Andrew Rozefelds with a modern pandanus and the fossilised fruit. Credit: Queensland Museum

It’s been named Pandanus estellae, after Bridgeman’s wife.

A description of the fossil, and the implications it has for our understanding of modern Pandanus, is published in the International Journal of Plant Science.

“The fossil record on the family is pretty poor,” says lead author Dr Andrew Rozefelds, principal curator at the Queensland Museum.

“The fossil fruits are surprisingly few and far between. In Hawaii, they’ve found very recent fruits that have fallen on to the magma. And they’ve left an impression of their fruit shape, but they’re basically modern fruits. As far as I can see, there were some fruits described from Europe that were Pandanaceae [the family] – but not Pandanus [the genus].

“So, this is the first Pandanus fruit that we’ve found essentially anywhere, that’s of any age.”

Rozefelds says that this fact alone leads to further intrigue.

Read more: Fossils suggest organisms diversified earlier than thought

“Why haven’t we found more? The fruits are quite hard and woody; why have they been missed? And you then go down a rabbit hole in terms of speculation as to what could be happening.”

Digital painting of knobbly green fruit in palm leaves
Artist Alison Douglas’ reconstruction of Pandanus estellae.

One of his theories leans on fruit size. Despite being a mature specimen, the fossilised fruit is much smaller than many modern Pandanus fruit.

This suggests that possibly Pandanus plants radiated out from Gondwana quite recently in an evolutionary sense, once they’d evolved to grow larger fruit which could carry their seeds to distant shores.

“In order to be successful in a marine environment, you’ve got to basically ensure that your seeds are kept dry and protected from being immersed in the seawater,” says Rozefelds.

“And that’s why they’ve gone down this pathway of larger, fruit size. But that’s all speculation – I can’t prove any of that.”

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