It may look innocuous, but this deadly nightshade berries can be fatal. (Credit: Donald Macauley/Wikimedia)

Australia's most poisonous plants

  • BY Sylvia Varnham O'Regan |
  • July 04, 2012

They may seem innocuous, but some plants can be deadly. Here are some of the most poisonous in Australia.

ON THE FACE OF IT, plants may seem innocuous, but some of them can be surprisingly lethal to humans who may come across their path. Because plants cannot run away from their predators, they develop toxicity as a defence. Often shoots are very high in concentration of poison and can be more harmful if consumed. Toxicity usually increases with rising carbon dioxide and plants are more toxic during a drought.

About 1000 species of plants in Australia are known to be toxic to animals and humans and plenty more cause skin and eye irritation, rashes or discomfort. About 10 per cent of plants in Australia even make cyanide. Plants vary from region to region, but no matter where you are you need to know what to keep an eye out for.

Dr Marco Duretto, Manager of Plant Diversity at the Royal Botanic Gardens and Domain Trust in Sydney, says if you're in the bush or just rummaging around the garden "do not put things in your mouth unless you know what they are, because there a lot of toxic plants out there".

However, it's difficult to determine what plants pose risks to humans because of a lack of information about the effect of many plant species on humans, says Jeff Robinson from the Victorian Poisons Information Centre at Austin Hospital in Melbourne.

"A lot of literature refers to plants poisonous to animals," says Jeff. "It's something to go by but doesn't necessarily mean that the same will apply to humans."

There are also many variables that make distinguishing poisonous plants and their risks difficult. "There is seasonal variation in terms of the content of the poisons in the different parts of plants," Jeff says. "Leaves and flowers may have different amounts of poison, for example."

But there are a few well-known toxic plant species that humans should avoid. 

Gallery: Australia's most poisonous plants

Plants can talk to each other: Day of the Triffids for real
Gympie-Gympie plant: once stung, never forgotten
Sun rises on tequila plant harvesting for biofuel
Can we use native plants to predict floods
Seed back protects the world's plant species
World's first night-flowering orchid discovered