boab tree
© Kevin Smith
Boabs are a striking tree that grow in many parts of the Kimberley and a small area of the Top End.
They are striking, fat-trunked trees unique to parts of the Kimberley and a small section of the Top End, but two scientists studying how they came from Africa or Madagascar have widely different explanations.

If you've ever seen a boab tree you don't need to be a botanist to realise something strange is going on.

Their trunks are swollen and wrinkly - as if someone has planted an elephant which has sprouted into a tree.

They are so unlike any other Australian tree that you can't help but wonder where they came from.

But if you see an African or Madagascan baobab then it's immediately apparent there has got to be a connection there.

But why does an Australian tree have its closest relatives on the other side of the Indian Ocean?

It's a question put to Curious Kimberley by Kununurra resident Maria Bolton Magnay.

"My question for Curious Kimberley is about the boab trees that we have here in the Kimberley, and how it is they came from Africa to Australia. What's the connection?"

Maria has family in Africa, and she had wondered why African and Madagascan baobabs are more like Australian boabs than any of these outlandish trees are to plants in their immediate neighbourhoods.
boab
© Philip Sproull
Boab trees are renowned for individual shapes and character.
Science disputed

Two scientists have applied modern genetic research to the question of how boabs got to Australia and they have come up with widely different answers.

University of Wisconsin-Madison professor David Baum is a botanist who has studied boabs and baobabs for more than 30 years and he says that despite decades of research we still cannot say how boabs came to be in Australia.

"We're doing genomic analyses and what is remarkable is that you'd think that the more data you get the clearer the picture would become," Dr Baum says.
"The more data we get the more clearly we have an unresolved story."
But emeritus professor of physiology Jack Pettigrew, who started his academic life studying brains but for the past decade has been working on boabs, passionately disagrees, saying his research shows a clear result with extraordinary ramifications for the story of how people first arrived in Australia.

"They were brought here by people, and of course to prove that you need to know that they got here fairly recently," Dr Pettigrew says.

It's a radical and not widely accepted theory that brings the arrival of boabs forward in time and pushes the arrival of people to Australia even further back than the currently accepted 65,000 years ago.

Tectonics, floating, or people?

Dr Pettigrew's suggestion that people brought the boab to Australia is the most recent of three theories for how they got to Australia.

As plate tectonics and the idea that continents have joined and separated over millions of years became widely accepted in the 1960s, a connection between African and Australian plants seemed to have been solved.

Australia and Africa had been a part of Gondwana, a southern super-continent that split into the world we know today, with related plants such as Africa's proteas and Australia's waratahs seen as living evidence of the ancient union.

But one thing Dr Pettigrew and Dr Baum do agree on is that baobabs and boabs are not connected because of their Gondwanan history.
boab 3
© David Baum
Dr David Baum has studied baobabs in Africa and Madagascar as well as boabs such as this one known as the Wyndham boab prison tree.
This is because Africa was well separated from the rest of Gondwana 80 million years ago, and both scientists have found genetic connections between the boab and baobabs much more recently.

Although Dr Baum's research has not settled on an amount of time since boabs were connected to baobabs, his work suggests it is at least a few million years ago and maybe more than 10 million.
"My own estimates would say that it probably might even be double digits, that's millions of years, so well before humans were moving around," Dr Baum said.
So boabs are too recent to be Gondwanan but too old to be carried by people, according to Dr Baum, which is why he believes the most likely explanation is that a boab nut floated across the Indian Ocean millions of years ago.

"People have found the African baobab on Aldabra, which is an island really in the middle of the Indian Ocean," Dr Baum says.
boab 4
© ABC Kimberley: Ben Collins
Dr Jack Pettigrew has been researching when the Australian boab separated from its relatives like this African baobab.
Human migrations

But Dr Pettigrew believes that not only would a boab nut become waterlogged and sink before it crossed the Indian Ocean, his genetic research shows the boab came to Australia much more recently and was probably brought by people.

"The calculations tell you it's 72,000 years," Dr Pettigrew says.

The idea that the boab arrived just 72,000 years ago makes it plausible that the first humans to come to Australia may have brought the boab from Africa.

And the date ties into some other theories about human movement, including one of Earth's largest volcanic eruptions that may have driven migration at that time.
"So 72,000 years is pretty much close to what you would have predicted if it was a migrant that was leaving the famine that was caused by Toba in Africa," Dr Pettigrew says.
But this idea is controversial, so much so that the genetic calculations used by Dr Pettigrew to arrive at the 72,000-year figure have not been accepted by what he calls "established botanists".

Aboriginal knowledge

Robert Dann runs a tourism business in the Kimberley, introducing people to the plants he grew up eating and using from childhood.

"We were brought up eating the boab as kids," he says.

The pith inside the boab nut could be eaten ripe or cooked while it was green into a kind of porridge.

The roots of seedlings are eaten like a carrot, the young leaves are edible, and water can be extracted from the fibrous wood.

robert dann

Robert Dann says traditional Aboriginal culture says the boab was always in Australia.
Mr Dann laughs when he hears that scientists can't agree on how the boab came to be in Australia.
"I've always known that the boab has always been in the Kimberley," Mr Dann says.
"Aboriginal people never give a name to a fruit unless it's been here for thousands and thousands of years."

And there is a small chance that the Aboriginal belief that the boab originally comes from Australia could be the answer the scientists will eventually arrive at, according to Dr Baum.

"The prevailing wisdom has been that they probably got to Australia from Africa or Madagascar," Dr Baum said.

"There is a remote possibility, however, that the migration direction is the reverse.

"There were some fossil pollen of related groups found in Antarctica, only a few years ago, which just raises the possibility that the group may have started in Australia and migrated westward to Africa and Madagascar."
Who asked the question?
maria magnay
Maria Bolten Magnay lives in Kununurra in the East Kimberley where she designs jewellery, including boab designs, for her family jewellery shop. With family connections to Africa, Maria noticed the similarities between Australian boabs and African baobabs and wondered what in the world could explain the link.