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Australia’s stinging trees: please don’t pet them



The lore covering Australia’s huge stinging trees of the genus Dendrocnide is perhaps as dubious as it is vast. There have been countless nightmarish encounters with the needle-shaped hairs of its leaves injecting a poison that has driven men mad and caused horses to throw themselves off cliffs.

Some of these stories are centuries old and cannot be verified. But as Edward Gilding can attest, these legends contain at least one tidbit of truth: the absolute agony of being stabbed by the fine, downy hair that adorns the leaves and stems of Dendrocnide. The trees, which can grow taller than 30 meters, are found in the rainforests of Eastern Australia, where they torment hikers.

“It’s like pushing a nail into your flesh,” said Dr. Gilding, a biologist at the University of Queensland and a self-described sting expert.

The sting from the hair of the trees also has immense stamina, causing fear in waves for hours or days. Some anecdotes have reported months of intermittent pain; Some particularly bad stings have even taken people to the hospital.

For most victims, such persistent misery could be enough incentive to avoid the plants. But Dr. Gilding and some like-minded masochistic colleagues have instead worked to decipher what gives Dendrocnide its punch.

Dozens of experiments and countless stitches later, they identified some of the ingredients involved. As they reported in Science Advances on Wednesday, Australia’s stinging trees are filled with a toxin that, when injected, clings to pain-sensing cells of the recipient, messing them up, locking the affected area in the molecular equivalent of an infinite scream.

“So many things cause pain, and so little is known why,” said Isaac Chiu, a neurobiologist at Harvard University who was not involved in the study. Dr. Chiu noted that the tree’s toxins target a molecule found on nerve cells that is “fundamental to mammalian pain,” he said. “If this reveals something blocking that, it would be really exciting.”

The painful potency of dendrocnide plants has bothered researchers for decades. The trees harm people so often that many of their habitats are marked with warning signs warning inattentive visitors “to beware of the stinging tree”. People who visit these forests sometimes wear respirators, heavy-duty gloves, and a handful of antihistamines.

But even scientists motivated enough to inject themselves with extracts from the toxins of the trees couldn’t figure out the source of the sting, said Irina Vetter, pain researcher at the University of Queensland and author of the new study.

These experiments, which are ethically gray, can no longer be done, said Dr. Cousin. But you, Dr. Gilding and her colleagues were still able to separate the chemical constituents of the toxin from two Dendrocnide species and make synthetic versions of the compounds in the laboratory. A very small protein found in both plants made mice lick and pinch where it was injected. The molecule was thrown at nerve cells and put the trigger-happy cells in an “on” position, forcing them to send out a flood of signals.

The researchers named the tiny pain-causing molecules gympietides as an homage to gympie-gympie, the word for stinging tree in the language of the Gubbi Gubbi, a group of indigenous Australians.

Dr. Vetter was amazed to find that the gympietids bore a remarkable resemblance to toxins produced by poisonous spiders and cones, which use the chemicals to incapacitate their unfortunate prey.

“These are three very different groups of organisms – spiders, cones, and now these trees – that produce a toxin that is very similar,” said Shabnam Mohammadi, a toxin researcher at the University of Nebraska-Lincoln who was not involved in the study was.

It is an impressive example of different branches of the Tree of Life converging on the same solution.

Researchers aren’t sure how the toxin will benefit dendrocnide trees. Perhaps it serves as some sort of chemical armor to ward off hungry herbivores, said Dr. Cousin. But some animals, like beetles and pademelons – petite relatives of kangaroos – seem to like to feed on dendrocnide leaves, stinging spines, and everything.

Dr. Chiu and Dr. Mohammadi both hypothesized that gympietide aren’t the only factors making dendrocnide toxin ingestion so difficult, especially given the plants’ bizarre and persistent side effects. Some of Dr. Vetter’s previous confrontations with the trees resulted in chest pain and stabbing discomfort in her extremities, among other things.

“I think they just scratched the surface of what these plants contain,” said Dr. Mohammadi.

Until more of these mysterious ingredients are identified, Dr. Gilding to stay away from stinging trees. “When you’re working with the plant, it’s next to impossible not to get stung,” he said.

This challenge is made more difficult by the inviting appearance of the facility, stated Dr. Gilding feast. The same hair that can create a dose of incredible pain makes the leaves and stems look deceptively soft and felty. “As if it was a furry, friendly green plant that you want to rub,” he said.

If it’s not yet clear: Don’t.


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