Buying back a dairy farm 50 years after it fell out of the family has sparked a mystery that is proving to be a tough nut to crack.

The dairy has a single indigenous macadamia tree growing in an area not known for Australia's native nut.

The tree's origin has long been known — planted by the property owner's father nearly a century ago — but where the original nut came from has always remained a mystery.

These days beef cattle graze on the rich pastures near Way Way Creek, 12 kilometres south of Macksville on the New South Wales mid-north coast.

Standing firm overlooking a dry watercourse in one of the paddocks is the macadamia tetraphylla, one of Australia's two edible varieties of indigenous macadamia trees.

It was planted by Neil McLeod's father on the family property, which was one of the area's first dairies.

"My dad cared for it. It was a pretty rare tree," Mr McLeod said.

"Macadamias were sort of unknown that long ago and here it is now still alive," Mr McLeod explained while standing next to the tree he knew as a boy.

Mr McLeod left the property, studied marine engineering and ended up living in Queensland. The property then went out of the family.

It came back on the market several years ago, and Mr McLeod and his wife decided to go and watch the auction.

"I didn't intend on buying the farm. However, I put my finger up and ended up with it," Mr McLeod said.

The tree has sparked interest for people such as Denise Bond, the chief executive officer of the Lismore-based Macadamia Conservation Trust.

The variety is usually found further north — between the Richmond River in northern New South Wales to just past Bundaberg in Queensland.

The indigenous macadamia planted nearly 100 years ago towers over Neil McLeod who bought back the family property. ( Supplied: Gwen McLeod )

"Because macadamias grow in dense forest often right down in the gully area of creeks, they could be tucked away in areas that haven't been found," Ms Bond said.

"So even though we have what is the known distribution, I think it is impossible to say that it is absolutely the limit to their range."

Mr McLeod wondered if the nut may have been picked up by timber workers plying their trade alongside the creek running through the dense rainforest overlooking the family farm, and later found its way into his father's possession.

Research being conducted by Southern Cross University enables DNA analysis to determine if the nut, which led to the tree, may have been from nearby.

"I don't think you can discount it, until you have done a really close search of the area. A lot of investigation of plants have been done for specific purposes," Ms Bond said.

"In one forest area you may know what trees are there, but someone may not have bothered to look at all the other species.

"It would be good to get a botanist out there to have a really good look to see if there is anything there."

More trees on the way

While the tree's origins had sparked interest, Mr McLeod and his wife have three healthy macadamia tetraphyllas, which they have propagated from the tree planted by his father.

They have produced a pink flower, not unlike what many would confuse for a bottlebrush, which goes on to be the much sought-after nut.

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While the tetraphylla may be only one of the two indigenous edible macadamias, it is the integrifolia that was largely the basis for commercial varieties producing the in-demand nut.

Mr McLeod believed the tetraphylla could be attractive if produced for commercial purposes.

"They are a beautiful fruit — they are somewhat sweeter than the macadamias we are used to these days," he said.

His liking of the nut was backed up by the many black cockatoos in the area.

"We don't get that much of a chance to sample the nuts from the young trees," Mr McLeod said.

"The cockies sit on the nearby fence, licking their chops, waiting for the nuts to mature."