Queensland researchers are shocked to discover the global macadamia industry may have originated from nuts from a single tree or small number of trees, taken from Queensland to Hawaii in the 19th century.

Given the lack of genetic diversity in the $3 billion crop, the race is on to preserve wild macadamia trees to improve traits like disease resistance, size and climate adaptability.

Southern Cross University's Dr Cathy Nock said the discovery back to Queensland was startling.

"It was a bit of a shock to see just how narrow the gene pool was from which the Hawaiian cultivars were developed.

"They represent about 70 per cent of the trees that are grown in orchards around the world."

How the great trace began

University of Queensland scientist Craig Hardner says this Brisbane beauty is the oldest known cultivated macadamia tree in the world. ( Supplied: University of Queensland )

University of Queensland horticultural science researcher Dr Craig Hardner used his Churchill scholarship to collect DNA from commercial macadamia orchards in Hawaii.

He traced their ancestry all the way back to a tiny patch of wild trees which still exist on private property at Mooloo, near Gympie in south east Queensland.

"A small collection of seeds were taken to Hawaii at the end of the 19th century and historical records suggest that there was maybe six trees grown from that sample of nuts that were taken by Robert Jordan and planted in his brothers' backyard in the suburbs of Honolulu in 1896," Mr Hardner said.

"Then when Hawaiians became aware of the delicacy of macadamias they thought that it was a good new crop to use for commercial production."

In collaboration with the Macadamia Conservation Trust, Healthy Land and Water and Brisbane City Council, the researchers have collected hundreds of DNA samples from wild trees in their native habitat of northern New South Wales and south east Queensland, as well as old trees in backyards.

Macadamia Conservation Trust chair Paul O'Hare, Mary Burton and Andy Burnside at the birthplace of most of the world's cultivated macadamia trees. ( Supplied: Southern Cross University )

Crop clones

Southern Cross University's Dr Nock said there was little diversity in the macadamia crop.

"Like many horticultural tree crops, macadamias are grafted, so if you fly over the Bundaberg area or north eastern New South Wales you'll see thousands of trees but there's really only a handful of actual individuals," Dr Nock said.

"They're all clones, so there's very little diversity in the orchards, all the diversity that could be used for future improvement of the crop is still in the wild."

The United States, Australia, South Africa and Kenya are the world's largest producers, with China, South East Asia, South America, Malawi and New Zealand all now growing crops.

The oldest known cultivated macadamia tree stands in the Brisbane City Botanic Gardens and was planted by its first superintendent Walter Hill in 1858, not long after macadamias were discovered by Europeans.

Native to Australia macadamias are now farmed in countries around the world. ( Supplied: University of Queensland )

Their native sub-tropical rainforest habitat has been decimated by clearing and development and of the four wild macadamia species, three are listed as threatened and one is endangered.

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Two of the native species are smaller, meaning their genetics could be used to reduce the size of macadamia trees in plantations, making them easier to manage and harvest.

"There's this amazing amount of diversity that's evolved and adapted over probably 30 million years that's there that we can use in future," Dr Nock said.

She added it was very rare to be able to pinpoint the origins of a crop's domestication.

"We're in a really enviable position because if you look at the domestication history of most other crops you go back thousands of years, so it's often difficult to find wild populations that still exist and if they do they've often been subject to gene flow from the crop so they're not pure wild populations anymore."

Wild macadamia hunt

Macadamia Conservation Trust executive officer Denise Bond says it is crucial that wild macadamias are protected. ( Supplied: Macadamia Conservation Trust )

Macadamia Conservation Trust executive officer, Denise Bond, said the hunt continued to find and preserve as many old and wild trees as possible and urged people to get involved.

"There are some big patches in our lovely national park and state forest areas like Amamoor and Conondale and the Tweed Valley but there also little pockets surviving on private land and even in people's backyards and farming land.

"Those are the ones that we'd like to protect before they get completely cleared."

She said the plants also faced threats from smothering invasive weeds like cats claw creeper and madeira vine.

A smothering vine had to be cut from this wild macadamia tree at Amamoor. ( Supplied: Macadamia Conservation Trust )

"We really want people to be vigilant about keeping those out of macadamia habitat and protecting the habitat and making sure that people know that south east Queensland and northern New South Wales are the only places in the world where macadamias grow in the wild."

Every new discovery of wild macadamias was exciting to the team because the trees could breed within two to three kilometres of each other.

"So every time we find a new population it's a potential stepping stone that joins up the other trees so that they can still be living and evolving as they would in the wild.

"If there's a network of them throughout the landscape they'll maintain the population dynamic that keeps them being a viable species.

"We love to find out where they are."