Eucalyptus could become a prospector's best friend: a team of researchers say they've proven once and for all that some trees' leaves contain tiny gold particles drawn from deep underground. In a study published in Nature Communications, a group led by Melvyn Lintern of Australia's national science agency CSIRO tested both lab-grown and wild eucalyptus trees for evidence of gold. Microscopic particles have been found before in leaf samples, and researchers have successfully grown plants that absorbed gold through their roots. But the researchers say these studies use gold concentrations higher than anything you'd find in the natural environment, and they rarely focus on the kind of plants that could actually be used to look for gold. Without evidence to the contrary, it wasn't possible to rule out theories that traces of gold were just deposited along with all the other dust that's swept onto eucalyptus leaves.

The team looked for particles of gold growing directly in the leaves

The researchers looked at eucalyptus trees at the Freddo Gold Prospect in western Australia, which has higher than average gold concentrations but is undisturbed by mining. The team collected leaves growing directly over the deposit and from successively further away, then punched out samples and studied them for particles of gold growing directly in the leaves. While concentrations were generally low, they spiked in leaves from trees that were growing on the deposit. Back in the lab, the group grew separate groups of eucalyptus trees in soil with high concentrations of gold and no gold at all. The particles found in leaves from the former appeared similar to those over the naturally occurring deposits, making the connection stronger. Eucalyptus trees, the researchers believe, are drawing gold from 35 meters below ground, then pushing it out to the leaves to reduce its poisonous effects.

The actual amount of gold in each leaf is negligible: Lintern has described the particles as so small that the leaves from 500 trees over a deposit would only be enough to make a wedding ring. But this means that golden eucalyptus trees can indicate where miners might want to look. As the researchers note, a study earlier this year found that gold discovery had dropped sharply over the past decade and new sites have become progressively more expensive to find, raising concerns that there won't be enough mines to replace the old ones as they run out. But eucalyptus leaves could serve as a naturally occurring sample collector, bringing minerals from over a hundred feet underground high into the air.