• Roasted and sliced black bean seed. (Royal Botanic Garden Sydney.)Source: Royal Botanic Garden Sydney.
A mystery as to why random clumps of a east coast rainforest tree are found high up in parts of the Great Dividing Range appears to have at last been solved.
Staff writers

14 Nov 2017 - 10:45 AM  UPDATED 14 Nov 2017 - 10:49 AM

A new study has revealed Australian Aboriginal groups helped the spread of edible plants by hand long before Europeans arrived.

The research on rainforest tree Castanospermum australe or black bean, reveals through DNA testing that isolated populations of the black bean tree, which were found far inland up mountainsides, were brought there by Aboriginal groups who used the seeds for food.

Botanist Maurizio Rosetto from the Royal Botanic Gardens in Sydney said that he was researching the genetic diversity of the disparate populations when he made the discovery that they had unusually low genetic diversity, coming from a single mother seed.

"Studying the DNA of plants allows us to look back in time to track evolutionary pathways and reveal many exciting and surprising stories from the past”. 

It's the first time a genetic study has been used to map a non-cultivated species of plant.

“We still have a lot to learn about how plants and people have influenced each other in Australia over tens of thousands of years," said Dr Rosetto.

Black bean trees are common in old growth forests and can grow up to 40 metres high. There is evidence Aboriginal Australians have been using them for at least 2500 years.

The heavy seeds are salt tolerant and float along watercourses before germinating in new locations. Scientist were initially puzzled as to why isolated populations were found growing at high altitudes.

The seeds are toxic to humans if consumed raw, so they require extensive preparation before consumption.

The locations of the plant matched those of trade and travel routes of Indigenous people along the east coast who carried and shared the seeds along those routes with other groups.

"Many of our ideas about traditional lifestyles and interactions with nature are being challenged by genetic information," said Dr Rosetto.

The study's authors looked at dreamtime stories, songlines and oral histories as part opf their research.

"We reveal anthropological evidence for prehistoric Aboriginal-mediated dispersal by verifying that: Aboriginal people used the species; and several sources including Songlines (Dreaming tracks) describe the deliberate movement of this species by Aboriginal people," the study said.

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