Gympie Gympie: One Sting, YEARS of Pain (Dendrocnide moroides)

[00:00:00]Hello everyone, and welcome to the Flora Files, where we dive into the world's most fascinating plants and fungi, one species at a time.

[00:00:07]I've had quite a few requests for this species, and I understand why.

[00:00:10]>> [music] >> It has a reputation for being the plant with the most painful sting. Some people have described it as being burnt with hot acid and electrocuted at the same time. The pain can last months, and in some accounts, years. This, of course, makes most coverage of this plant rather sensationalized, but here we're going to look at the biology, [music] the chemistry, and the history of this intense plant. And yes, it's from Australia, because, of course, it is.

[00:00:36]>> [music] >> The notorious tree being covered today is Dendrocnide moroides. The genus Dendrocnide comes from two Greek roots.

[00:00:45]Dendron, meaning tree, and cnide, meaning nettle. Moroides comes from Morus, which is the genus name for mulberries. So, we have the mulberry-like stinging tree. The fruits are edible, but that's if and only if you take care to remove the stinging hairs. Not something I can recommend It is in the family Urticaceae, which is the nettle family, and the family name itself comes from the Latin urere, meaning to burn. You can guess what the plants are known for. The most popular common name is gympie-gympie, which comes from the Gubbi Gubbi people of southeastern Queensland. Other common names include the stinging tree and stinging bush. Physically, Dendrocnide moroides is a perennial shrub or small tree, typically fruiting and flowering when under 10 ft or 3 m tall, though capable of reaching about 33 ft or 10 m tall in the right conditions. It has large heart-shaped leaves with serrated edges that can be 4 and 1/2 [music] to 8 and 1/2 in or 12 to 22 cm across.

[00:01:43]The stem, branches, petioles, leaves, and the fruit are all covered in stinging hairs. The hairs are technically called trichomes, which are highly modified surface structures that look, >> [music] >> under magnification, like hypodermic needles. They kind of are, since they are made of silica, are around 5 mm in length, are hollow, and have a very fine brittle tip. When the tip makes contact with skin, it snaps off cleanly, leaving the glass shaft embedded in [music] the skin, giving toxins a clear pathway to flow directly into the tissue. As you might imagine, these trichomes can get really stuck in the skin and release more toxins every time they are irritated. And because this is a spiteful Australian [music] tree, pretty much anything from a gentle breeze to just thinking about it can cause it to be irritated. [music] All joking aside, anything that causes a trichome to shift, even slightly, causes it to release more toxins into the surrounding tissue, causing even more irritation and damage. This is not something to wait to remove later. You want it out as soon as possible. The current best method of removing the trichomes is wax strips, like [music] the kind used for hair removal, since they can physically pull the shafts out of the skin.

[00:02:47]Wax strips or similar sticky products are now listed as an essential component of first aid kits in field research settings where the plant is found.

[00:02:55]Researchers working near the plant wear respirators alongside full arm and body coverage because the trichomes are fine enough to become airborne when the plant is disturbed, causing respiratory irritation, runny nose, nasal bleeding, and throat symptoms even without direct contact. I mean, do I need to say the phrase inhaling a bunch of tiny toxic needles is a bad idea? But I guess that also gets us to the next question. What makes the toxin of this tree so angry?

[00:03:21]Even if you remove the trichomes, people have reported continuing to feel pain for months. I've been stung by North American nettles before and it's not this bad. Sure, I took a stinging nettle to the knee and couldn't walk for 15 minutes. Yes, that really happened and this is not a Skyrim reference. But after it wore off, I was fine aside from the emotional damage. And while it's fun to make jokes, I'm sure just growing in Australian soil isn't enough to turn a nettle into a super nettle. So, let's dive into the chemistry. Until very recently, researchers assumed the pain mechanism of Dendrocnide moroides was similar to others in the nettle family and included a combination of compounds like formic acid, [music] histamine, acetylcholine, and serotonin.

[00:03:58]In fact, some of these compounds were identified in early analysis of the plant. The problem was that none of them could fully account for what people were actually [music] experiencing. Sure, histamine and formic acid cause pain and inflammation, but they don't cause pain that lasts [music] for months. They certainly don't cause pain years after the initial contact. Like I said, I was fine after about 15 minutes after an encounter with stinging nettle, and that's typical story, but still quite different from encounters with gympie gympie.

[00:04:25]A compound called meroide was isolated from Dendrocnide moroides, but it also failed to produce the characteristic symptom pattern [music] when injected in controlled experiments. So, something was being missed. Finally, in 2020, a research team at the University of Queensland discovered what it was. They were studying the closely related giant stinging tree, Dendrocnide excelsa, [music] took extracts from the trichomes and separated them into individual molecular groups.

[00:04:50]One isolated group caused significant pain responses in laboratory testing.

[00:04:54][music] When they characterized it, they found a small family of related mini proteins that were only 36 amino acids long >> [music] >> and had not previously been seen anywhere in the plant kingdom. They naturally named them gympi tides, because why wouldn't you? What makes gympi tides unusual is their structure.

[00:05:10]The shape they fold into is structurally similar to the toxins found in spiders and cone snails.

[00:05:16]So, while they are not related by ancestry, they still all evolved a way to inject toxins into animals. Does this make Dendrocnide moroides a venomous plant? I think it's fun to say so, [music] since it fits in with the, of course, Australia narrative, especially since the toxin is a neurotoxin, because of course a tree needs a neurotoxin.

[00:05:34]Why? Anyway, the mechanism of the toxin is how it interacts with the voltage-gated sodium channels in the nervous system. These channels, along with the sodium and potassium that flow through them, is how your nervous system sends [music] signals. How you tell your hand to move and how it tells you that that stove top is too hot. As you can imagine, messing up this pathway [music] is going to cause problems. Painful ones in this case. The sensory neurons involved use these channels to send pain signals with the shortest explanation being closed channels [music] means no pain and open channels means pain.

[00:06:06]Normally they cycle back and forth as the need arises. And as you might guess, gympie tides lock the sodium channels open. This means the cells can't turn off the pain [music] signal. And because the gympie tides are extremely chemically stable, they continue to do this for as long as they remain in contact with the nervous tissue, which as we know can be many months.

[00:06:24]The phenomenon where a light touch reignites the pain weeks after the original sting is not caused by trichomes that are still present. This was a belief basically until the 2020 paper that demonstrated it is the gympie tides. Removing the trichomes is still hugely recommended since it at least lowers the injected dose of gympie tides, but it does not remove the gympie tides that have already been delivered into the tissue.

[00:06:46]Those are still binding to sodium channels, ready to send a pain signal anytime those neurons fire. The discovery of gympie tides has now opened two significant research directions. The first is better treatment. Currently there is no antidote to a dendrocnide sting, but by understanding the exact mechanism by which gympie tides [music] lock sodium channels open, we are now at least one step closer to developing a targeted intervention.

[00:07:09]Some other compound that could compete with or displace the gympie tides from the channel binding sites. Something that could restore normal function. That work is currently ongoing. The second is pain science more broadly. Gympie tides represent a novel way of regulating the pathways that signal pain. Compounds that can do this are scientifically valuable precisely because they help map how the nervous system works. And if we can figure out how to disrupt it, then perhaps we can expand this knowledge to other treatments for chronic pain conditions [music] that have nothing to do with stinging trees. Since there are plenty of conditions where the normal pain switching off mechanism [music] fails. Another crazy note about gympie tides, a dried herbarium specimen of Dendrocnide moroides from 100 years ago retains viable gympie tides, which means museum collections containing this plant carry active sting [music] risk. And what does it feel like if you are stung?

[00:07:59]Well, I assure you there are plenty of sensational videos on YouTube you can watch where people are willingly stung by this plant.

[00:08:05]>> [music] >> Instead, I'm going to cover an account by Ernie Rider, who was a conservation officer with the Queensland Parks and Wildlife Service. He was slapped in the face and torso by the foliage in 1963.

[00:08:16]He said, "I remember it feeling like there were giant hands trying to squash my chest. For two or three days the pain was almost unbearable. I couldn't work or sleep, then it was pretty bad pain for another fortnight or so. The stinging persisted for two years and recurred every time I had a cold shower."

[00:08:31]That account definitely puts this plant on the do not hug list.

[00:08:35]There are stories about the sting being powerful [music] enough to be fatal to humans, but similar to the manchineel, this is not what is shown in modern clinical accounts.

[00:08:43]But as also pointed out by several commenters in the manchineel video, symptoms that are survivable today, thanks to modern medicine, may not have been easily survivable hundreds of years ago. So, beyond its in Australia, where exactly is this plant found and what is its ecological role? Dendrocnide moroides occurs in and near rainforest from Cape York Peninsula south to northern New South Wales. It is an early colonizing species in rainforest [music] gaps. Where a tree falls, where a road or track has been cleared, where logging or cyclone damage has opened the forest, that is where Dendrocnide moroides appears first [music] and fastest. This pioneer role is very important since early colonizing species in tropical rainforest gaps help stabilize [music] bare soil, accumulate organic matter, provide habitat and food resources for wildlife, and set the conditions to allow typical ecological [music] succession to continue.

[00:09:33]The fruit dispersal is primarily by birds, which are unaffected by the trichomes and eat the fruit [music] freely.

[00:09:39]And yes, I was just as annoyed and amazed reading that as you were hearing it.

[00:09:42]>> [music] >> The white nymph butterfly uses the plant as a larval host species. Nocturnal beetles have been documented feeding on it. So really, it's [music] a plant that is absolutely great for the environment, just not for mammals. And there you have it, Australia's monster tree that came up with its own novel neurotoxin. But as a pioneer species and a provider of a new area of research for our own medicines, it is more than just a scary prop. If you've made it this far, I hope you enjoyed this dive into the story behind the notorious gympie gympie.

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