The discovery of stingless Gympie-Gympie trees could mean the plant is adapting to life without a big predator. Image Credit: Hugh Spencer

Gympie-Gympie losing its sting?

  • BY Lydia Hales |
  • February 06, 2014

Is one of Australia's most painful plants losing its sting?

THE GYMPIE-GYMPIE STINGING tree (Dendrocnide moroides) is generally considered to have the most painful sting of any Australian plant, but a chance finding at the Cape Tribulation Tropical Research Station suggests some trees may have lost their sting.
One day in 2006, when director of the research station, Hugh Spencer, volunteered to have the usually excruciating venom rubbed onto his skin, he expected overwhelming pain. Hugh has been stung countless times by the Gympie-Gympie (or what he refers to as "nettles on steroids"), either while testing a successful treatment for the stings or accidentally walking into the leaves.
Hugh was helping with research into the venom by then-student Vivian Kong Tse Lam, taking extreme while care collecting leaves from a tree growing by a road near the station. They were using high pressure liquid chromatography to separate the chemicals in the venom, as well as testing the reaction to samples on Hugh's skin.

But to his surprise, the walloping pain never arrived when a sample of the venom from this tree was tested on Hugh's skin. In disgust at the lack of results, he says, he went and rubbed the fresh leaf on his arm - only to find no reaction there either.

Unfortunately that tree was destroyed by the Council road crew, and another non-venomous tree they found was destroyed by cyclone Yasi, so the research is on hold.

Gympie-Gympie losing its sting? 

Scientists have determined the mechanism used by the stinging trees to deliver their potent punch - their stems and broad, heart-shaped leaves are covered in hollow silica hairs, which when touched, break off at the tip and inject venom. The hairs can cause long-lasting (in some cases for months and even years) intense pain, since they become embedded in the skin.

But the specific chemicals responsible for so much misery remain poorly-understood, hence Hugh and Vivian's interest. It's Hugh's estimation that a peptide called moroidin, together with a cocktail of common neurotransmitters such as histamine, are responsible for the pain.

In the case of the stingless trees, the stinging hairs were still present and the leaves looked identical to other potent trees. This indicates an adaptation in the chemical structure of the venom, or a physical change to stop producing it altogether.

Hugh's guess is there is no evolutionary benefit for the tree to produce venom if its original predator no longer feeds on it. Smaller creatures like insects and some native animals often eat the Gympie-Gympie without any harm.

Hugh is interested in continuing this research and is looking for more non-venomous trees, but a lack of any simple chemical test for the venom is slowing the progress. Other challenges include the need to find another researcher with interest in the venom and skills in the High Pressure Liquid Chromatography, as well as obtaining more funding.