Little Shop Of Horrors: The Australian Plants That Can Kill You

Australia is so famous for its dangerous creatures that visitors often arrive fearful that everything that moves is out to get them. In a land where snakes, spiders, shells and even one of the iconic mammals — the platypus — can bite or sting, should we all be worried about plants as well?

Plants around the world produce a staggering diversity of chemicals and many of these are potentially toxic to animals including humans, sometimes even upon contact. Many of these toxins have evolved to protect plant roots, leaves and unripe fruits from being eaten by herbivores, particularly insects and browsing mammals.

Australia’s toxic plants are not terribly appealing or nutritious for humans. If someone is poisoned, it’s usually accidental, and many victims are curious children.

There are many historical records of plant poisoning in Australia involving early explorers and settlers who were short of supplies or looking for new sources of food. Today, though, plant poisoning accounts for less than 1% of calls to poisons information lines in Australia.

Animals beware

The threat of poisoning to livestock is much more substantial and causes significant economic and animal welfare impacts.

It’s in the interests of cattle and sheep to become expert botanists, but even experts can get things wrong when confronted with something they’ve never seen before. Most livestock poisonings occur when animals are moving through new country or are put into new paddocks with unfamiliar plants.

Native plants that kill significant numbers of livestock include Cooktown ironwood in northern Australia (as little as 50 grams of leaf can contain a quantity of alkaloids that can kill a bull) and the poison peas and heart-leafed poison bush of Western Australia and Queensland respectively (Gastrolobium), which contain a deadly metabolic poison, sodium fluoroacetate.

Elsewhere, introduced pasture weeds such as fireweed, Senecio madagasciarensis, and Paterson’s curse, Echium plantagenium, pose significant threats to cattle, sheep and horses.

It’s in the dose

The adage that “the poison is in the dose” is correct in that small amounts of most poisonous plants are unlikely to cause permanent damage or death, although there are exceptions. Indeed, most herbivores have to tolerate some exposure to plant poisons because they’re so widespread among the plants they eat.

Small amounts of some toxic compounds can even be beneficial and sometimes have traditional or medical uses. Aboriginal people, for instance, used Duboisia hopwoodii and other native tobacco species (Nicotiana) to produce a powerful and widely traded stimulant, pituri, the active ingredient of which is the potent alkaloid, nicotine.

Similarly, atropine, an alkaloid found in Angels’ trumpets and thorn-apple (Brugmansia and Datura species) is a powerful hallucinogen and toxin. But it’s also a valuable drug used to treat some heart and nervous conditions, as well as poisoning by some other plant alkaloids and cardiac glycosides.

Knowing what dose of poison a plant contains is not always easy. How much toxin an individual plant contains can vary with season, the age of the plant, soil type, drought and the plant’s genes. Just as you may be tall and your next-door neighbour short, two plants of the same species growing alongside can vary in how much toxin they produce.

On top of that, different animal species and individual people and animals can also vary in their ability to tolerate poisons. This makes ingesting toxic plants a little like Russian roulette: there’s a strong element of chance.

Deadly relatives

A significant number of Australia’s more than 20,000 plants are potentially toxic. In many cases, Australia has species or subspecies of plants that are closely related to well-known toxic plants from elsewhere. But their relative toxicity is not well established.

The Indian suicide tree, Cerbera odollum, has been described as the “perfect murder weapon”, for instance, but the toxicity of our native Cerbera manghas is less well understood, despite the fact it possesses the same cardiac poisons.

Similarly, how our native strychnine bushes Strychnos lucida and S. psilosperma compare to the better-known strychnine tree S. nux-vomica from India is not well known, but they do also produce strychnine.

Unless you’re a hungry ruminant, you’re probably unlikely to suffer death by plant poisoning in Australia, but the risk is nonetheless real. It pays to realise that garden plants and even common indoor plants are sometimes just as dangerous as what lurks in the bush. Parents and outdoorsy types should be aware of the risks posed by contact with or ingestion of plants.

This article is part of our series Deadly Australia. Stay tuned for more pieces on the topic in the coming days.

The Conversation

Ben Moore, Senior Lecturer in Ecology, Hawkesbury Institute for the Environment, Western Sydney University

This article was originally published on The Conversation. Read the original article.

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    If you are talking dangerous plants then big gum trees that decide, "it's been a bit hot and I'm having trouble getting enough water. I guess I better drop a hundred kg branch now." should probably be mentioned

      have had this happen numerous times at my place.
      our neighbour heard a crack one morning while sitting on the toilet that scared her off of the toilet. 5 seconds later, a branch pierced her roof and smashed her toilet.
      the branch was one of my gums. its also dropped about 4 or 5 other sizable branches over the years, 2 since being dead-wooded and cleaned. wife still wants to keep the tree though, seeing we have already cut down about 8 or 9 gums for a sub division.
      i want it gone so i have more room for a new garage and carport, oh, and for safety reasons of course.
      ahhhh, environmental dilemmas vs human life dilemmas....

      Last edited 15/01/16 9:15 am

    The gympie gympie doesn't need to kill you... It makes you kill yourself.

      This. There's a video online of a guy doing a documentary on it, and after hearing how bad it is, he decides to brush the back of his hand on it for a split second for science. He then curls up in a ball and vomits because he's in so much pain.

      There's also that time around WWII where some military officer used a leaf as toilet paper, and then shot himself because the pain was so bad.

      Nasty stuff!

      Last edited 14/01/16 12:24 pm

        I think that last story about the 'toilet incident' is unconfirmed since it's always sounded like an urban legend. No citations for it on Wikipedia either I think.

        I love telling tourists about the Gympie Gympie though.

        Last edited 14/01/16 1:38 pm

          Edit: Skrybe beat me to it.

          While I'm at it... here's that video of the guy brushing his hand on it. What an idiot.

          Last edited 14/01/16 4:03 pm

          It is widely reported, but could be apocryphal. It was apparently mentioned by Cyril Bromley as happening around WW2, but that could be a pork pie.


          My parents are both from Gympie and my grandparents lived there most of their lives. I remember the story as a kid (back in the 70s). Pretty sure Dad told me as a warning not to touch the plant when we found some on Grandad's farm.

      Oh god this! I loved rainforests until I read up on the Steven King of plants species.

      Gympie Gympie is just not cool.

    I stupidly bit into the thick stem of a plant leaf on boxing day when I was a bit intoxicated. Whatever was inside burnt the inside of my mouth and left me feeling like I had gargled battery acid for two weeks. Good times

    It's in the interests of cattle and sheep to become expert botanists

    When I grow up, I'm going to bovine university!

      Don't kid yourself Jimmy, if a cow ever got the chance he'd eat you and everyone you cared about!

    Borrachero tree... Scopolamine! watch the VICE doco on youtube, you'll pretty much never want to go to columbia, ever. haha

    Borrachero tree... Scopolamine! watch the VICE doco on youtube, you'll pretty much never want to go to columbia, ever. haha

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