Australia has become an Internet meme because of the unique creatures that live there, including some of the world’s most venomous and lethal species. This danger has arisen in response to evolutionary pressures and the particular biotic and abiotic conditions of Terra Australis. Even the most adorable animal could pose a serious threat to our health, according to the jokes circulating on the Internet.
Australia is not only home to ultra-dangerous animal species. It is also home to what is surely the most poisonous plant in the world: Dendrocnide moroides. It is popularly known as stinging bush or tree, gympie-gympie in Aboriginal language, or with the suggestive name of suicide tree, which already invites to respect the distances.
This shrub is found in and around the rainforests of eastern Queensland and northern New South Wales. It often occupies the clearings left by dead trees in the rainforest, as it requires large amounts of light. It belongs to the Urticaceae family, the same as that of the common nettle, and 6 species are known in Australia. Of all of them, the most poisonous would be our protagonist.
Identifying traits
Here are some of its morphological characteristics so that you can learn to recognize it and stay away from it if you ever see it during your vacations in Australia or in a botanical garden (although in these cases it is usually covered by a screen). It is an evergreen shrub that can reach up to 3 m in height, with relatively large simple leaves. They are heart-shaped and have a serrated edge. The petiole is attached to the leaf blade at its edge, a characteristic feature that makes it easy to distinguish it from other species to which it closely resembles.
The fruit is reddish in color and is very reminiscent of blackberries, hence the epithet of its scientific name: “moroides”, that is, similar to the blackberry. Technically it is edible, but it is advisable to avoid it for what I will tell you below. The inflorescences arise in the axils of the leaves. This species is monoecious, which means that the male and female sex organs are born on the same plant, only in this case they appear separately on different flowers.
However, its most characteristic attribute is the tiny stinging hairs of siliceous nature that completely cover the plant. Although it would be more correct to call it trichome. They are found everywhere: stems, petioles, leaves, and fruits. Precisely, the toxicity of this plant lies in these tiny structures, no more than 7 mm long. That is why I launched before a warning in relation to the fruits: they are edible, yes, but only if the trichomes have been previously removed. Even so, it is better to be cautious and not to try it, because the most probable thing is that we will nail a few trichomes and we will be immersed in a real nightmare.
An indescribable pain
Few species have the questionable honor of having warning signs. If you go hiking in the regions inhabited by Dendrocnide moroides, it is very likely that you will encounter a sign along the way urging you to stay on the trails to avoid any encounter with the dreaded suicide plant. Better safe than sorry…
The toxicity of this plant is not to be taken as a joke. Being pricked by its trichomes translates into an unparalleled and prolonged suffering. Only a light touch is enough to be filled with trichomes. They are like hypodermic needles: are very sharp and hollow inside. Inside they harbor a cocktail of toxic substances that trigger the symptoms when they are inoculated into the skin. These chemicals are released when the trichome comes into contact with the skin and breaks along a fracture line near the tip.
The pain triggered by the toxins is possibly one of the worst and most intense pains a human being can experience. People have described such undesirable suffering as an initial stinging that progresses to an unbearable shooting pain, comparable to the sensation of an acid burn accompanied by an electric shock at the same time. The pain progressively intensifies over several minutes or hours depending on the severity of the prick and the amount of trichomes stuck. Subsequently, the agony shows clemency and moderately attenuates, now resembling a strong contusion. In the most severe cases, urticaria and swelling and intense pain of the lymph nodes occur. Another common symptom is acute paresthesia, i.e. tingling or numbness of the affected parts and nearby areas.
The nightmare does not end here. Pain and discomfort can persist for long periods, lasting for several days, weeks, or months. The trichomes are so thin and tiny that, when they penetrate the skin, they can become enveloped in it, making their removal practically impossible. In addition, their siliceous composition makes their degradation by the body extremely difficult. However, the real culprits of this long-lasting pain are the toxins. Specifically, a family of peptides called “gympietides” (after the aboriginal name of the plant). Their chemical structure gives them great stability, to the point that the leaves that have long been dried on the ground or those that are part of herbaria from decades ago are still toxic.
It is curious that both their structure and their mechanism of action are reminiscent of the poisonous peptides of some spiders, scorpions, or Australian cone snails. The toxins of these animals interfere with the correct functioning of the sodium channels of neurons. It is therefore possible that this is also the pathway by which “gympietides” generate pain, thus acting as neurotoxins.
After the acute pain phase, intermittent painful flare-ups may appear in response to various stimuli, such as pressure on the affected area, contact with water, temperature changes, etc. Thus, a pleasant relaxing shower can turn into a distressing and bitter experience.
Danger from a distance
The best way to prevent a danger is to keep your distance. In the case of the suicide plant, the greater the distance, the better, since it is not even necessary to touch it to get a ration of trichomes. It is enough to be close to the plant for a few minutes. The stinging bush is constantly releasing trichomes and they can remain suspended in the air thanks to their lightness. It is only a matter of time to breathe them in or swallow them and they will stick relentlessly in our mucous membranes. In the worst cases, inhaling trichomes can lead to severe respiratory problems.
Trichomes are a defense mechanism to repel herbivores. Sure it scares most of them away, but some animals have been able to circumvent this seemingly unbreakable line of defense. Several insects have been observed to feed on the leaves of this plant and, even more surprisingly, so does the red-legged pademelon (Thylogale stigmatica), a kind of miniature kangaroo. How it is able to withstand the excruciating pain of trichomes is still a mystery. The same cannot be said for domestic horses. There are known cases of horses that have accidentally come into contact with these plants and lost their temper. Some ended up losing their lives by falling down ravines, while for others the only viable solution was slaughter. Some birds also feed on the fruits, thus contributing to the dispersion of their seeds.
Distressing testimonies
Despite the agonizing torment caused by the suicide plant, it has caused few hospitalizations, and even fewer confirmed direct deaths. However, the dozens of accounts of encounters with this plant continue to highlight its danger. For example, an Australian conservation officer recounted the terrible suffering he experienced after an unfortunate encounter with this species. For three days he faced indescribable pain that prevented him from sleeping or working normally. Eventually, the pain subsided, but for the next two years he relived the prickling sensation every time he took a shower.
The brave ecologist Marina Hurley, who did her doctoral thesis on these plants, knows well what it feels like to touch or inhale the trichomes. During one of her doctoral investigations, she pricked herself with a dried leaf from the ground that rendered her hand useless. On another occasion, she breathed in the insidious needles by standing too long near one of these plants. She ended up suffering from intense sneezing, runny nose, and continuous tearing. To make matters worse, she eventually developed a serious skin allergy as a result of the contact.
During her investigations, Dr. Hurley had the opportunity to collect several testimonies. For example, a soldier told her that, during maneuvers, he fell on a stinging bush. The severity of the punctures must have been such that he was tied to a hospital bed for three weeks, unrestrained by the pain.
Another researcher recounted the ordeal he went through after the trichomes were stuck in his face. He felt as if acid had been poured into his eyes and suffered breathing difficulties due to swelling of his tongue and mouth. He ended up temporarily losing his eyesight and suffered a shock. Fortunately, he made a full recovery several days later.
Of course, his nickname “suicide plant” comes from the macabre stories about people who would have chosen to take their own lives rather than endure the venom of Dendrocnide moroides, although some of these stories seem fanciful.
To avoid adding more people to the list of victims of the suicide plant, the most reasonable thing to do is to take all possible precautions: avoid leaving the marked paths of the Australian hiking trails, respect the warning signs, keep a safe distance, and inform yourself in depth about this genus of poisonous plants. It is true that Dendrocnide moroides is an extremely interesting species from a botanical and ecological point of view, but knowing what we now know, it is best to appreciate it and be fascinated from a safe distance.
Para evitar engrosar la lista de víctimas del aguijón del suicidio, lo más razonable es tomar todas las precauciones posibles: evitar salirse de los caminos señalizados de las rutas senderistas australianas, respetar las señales de advertencia, mantener la distancia de seguridad e informarse en profundidad sobre este género de plantas venenosas. Cierto es que Dendrocnide moroides es una especie extremadamente interesante desde el punto de vista botánico y ecológico, pero sabiendo lo que ahora sabemos, lo mejor es apreciarla y fascinarnos desde una distancia segura.
REFERENCES
Burdon A (2009). Gympie Gympie: Once stung, never forgotten. Australian Geographic [online] June 16. Available in: https://www.australiangeographic.com.au/topics/science-environment/2009/06/gympie-gympie-once-stung,-never-forgotten/
Ensikat HJ, Wessely H, Engeser M, Weigend M (2021). Distribution, Ecology, chemistry and toxicology of plant stinging hairs. Toxins 13, 141. https://doi.org/10.3390/toxins13020141
Gilding EK, Sami S, Deuis JR, Israel MR, Harvey PJ, Poth AG, et al. (2020). Neurotoxic peptides from the venom of the giant Australian stinging tree. Sci. Adv. 6, eabb8828. https://doi.org/10.1126%2Fsciadv.abb8828
Hurley M. (2000). Selective stingers. ECOS Magazine 105, 18-23.
Hurley M (2018). “The worst kind of pain you can imagine” – what it’s like to be stung by a stinging tree. The Conversation [online] September 28. Available in: https://theconversation.com/the-worst-kind-of-pain-you-can-imagine-what-its-like-to-be-stung-by-a-stinging-tree-103220
Robertson PA, MacFarlane WV (1957). Pain-producing substances from the stinging bush Laportea moroides. Aus. J. Exp. Biol. Med. Sci. 35, 381-393. https://doi.org/10.1038/icb.1957.41
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