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Earth’s most poisonous plants
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Some common species that rank as the deadliest plants in the world

In 2014, a gardener on a country estate in the UK mysteriously died of multiple organ failure.

Pretty but deadly, the Aconitum or wolf's bane

The cause of his death remains unclear, but evidence suggested he had been killed by a popular flowering plant, a member of the buttercup family. The plant in question, called Aconitum, has blooms said to resemble monk’s hoods. But the plant is also known by other more sinister names; wolf’s bane, Devil’s helmet and the Queen of Poisons.

The most poisonous part is the roots, though the leaves can pack a punch too. Both contain a neurotoxin that can be absorbed through the skin. Early symptoms of poisoning are tingling and numbness at the point of contact or severe vomiting and diarrhoea if it has been eaten.

The manchineel tree, one of the worst untouchable species

The popular theory is that toxins have evolved in plants as a defence. In certain species, chemical compounds that are produced to fight off insect pests and other micro-organisms can do damage to big animals too.

One of the worst untouchable species earns the dubious honour of being the world’s most dangerous tree. The manchineel grows in northern South America and the Caribbean. In some parts of its range it’s painted with a cautionary red cross.

A notice that warns of the dangerous machineel tree

The milky sap produced by this tree contains the powerful irritant phorbol. Just brushing past it can leave you with horribly scalded skin. Burning down these trees is also a bad idea. The smoke from a burning manchineel can temporarily blind a person and cause significant breathing problems.

Castor beans from the Ricinus communis from which castor oil is made

When it comes to plants that shouldn’t pass your lips, one rises above the rest. Ricinus communis is a shrub that is praised for adding a dash of summer colour to gardens with green to purple foliage, palm-shaped leaves and distinctive spiky seed capsules.

Distinctive spiky seed capsules of the Ricinus communis

Castor oil, an acquaintance of anyone that needs to clear out their bowels in a hurry, is produced from the seeds of the plant. But so is ricin, which is extracted from the remaining residues of its seeds after the castor oil has been extracted.

Pretty foliage of the Ricinus communis

Ricin kills by interfering in cell metabolism, the basic chemical processes needed to sustain life. The creation of essential proteins is blocked, leading to cell death. Casualties can suffer vomiting, diarrhoea and seizures for up to a week before dying of organ failure.

The seeds of the rosary pea are bright red for a reason: the powerful poison, abrin, is made from them

A related poison, abrin is found with more of an obvious warning label. The seeds of the rosary pea are attractive bright ovals, often red with a black spot. Where they grow in tropical regions they are used to make bracelets, rosary necklaces or to adorn instruments. Abrin is similar to ricin but reportedly more powerful in its pure form.

Fortunately, death by plant poison is pretty rare in the age of modern medicine thanks to quick diagnosis and good supportive care. And many plant-derived toxins have to be purified to be lethal.

(All images - credit: Wikimedia Commons under Creative Commons licence)

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