10 Most Poisonous Plants in the World

As plants aren’t, by their nature, very mobile they have developed a variety of ways of protecting themselves from all things herbivorous. Many have evolved spikes, stings and even just an unpleasant taste. However, many went down the route of the ultimate deterrent – being so poisonous that anything eating them was unlikely to ever do so again.

Many of these deadly poisonous plants are the stuff of folklore and have alarming names such as Devil’s helmet,deadly nightshade, the little apple of death and the suicide tree. Whilst these would be enough to put any sane person off eating them I suppose it only helps if you know the name!

Jimsonweed is often listed on other websites as being deadly, along with other Datura plants. I have to say I’ve tried this one personally and lived to tell the tale. So whilst it seems this plant can be deadly, it’s not getting onto my list.

10. Oleander (Nerium oleander)

Oleander (Nerium oleander)

Oleander / Jericho rose (Nerium oleander)

Originally native to Asia, the Jericho rose or oleander is now common throughout Mediterranean regions and is a popular decorative plant in North America. The Italian name for oleander translates as ‘ass killer’, which should be enough to put anyone off eating them! If you did eat a sufficient does then you would start feeling those ‘ass killing’ effects almost straight away with a combination of cardiac and gastrointestinal symptoms. Bloody diarrhea, vomiting, drooling and irregular heart beat may all occur and swift treatment is essential. Toxins such as cardiac glycosides, nerioside and oldendrin all contribute to oleander’s lethal armory.

The whole oleander plant is poisonous right down to the nectar. It is said that even the smoke from burning the plant is toxic and there are reports of serious poisoning resulting from using the twigs as cooking skewers. What constitutes a lethal does seems uncertain with some stating as little as one leaf. Another source states 100 grams (3.5oz) is enough to kill a fully grown horse.

9. White snakeroot (Ageratina altissima)

White snakeroot (Ageratina altissima)

White snakeroot (Ageratina altissima)

It is believed that white snakeroot (Ageratina altissima) was responsible for the death of American president, Abraham Lincoln’s mother. She died of what was termed milk sickness which occurred as the result of drinking milk that was tainted with toxins from plants eaten by cows. In the early 19th century thousands of European settlers died in Midwestern America. It was only when a real life Dr Quinn (Anna Bixby) learnt about the properties of snakeroot from an elderly Native American woman that the cause was discovered.

The cause of the toxicity is a type of alcohol, tremetol, which gets its name from the tremors it causes in those poisoned. Along with this there would be violent vomiting, delirium, severe thirst and ultimately death.

The name snakeroot comes from the fact it can be used as a treatment when applied to snakebites.

8. Manchineel (Hippomane mancinella)


Manchineel Tree (Hippomane mancinella)

Manchineel Tree (Hippomane mancinella) Photo: Scott Hughes / License

Bearing fruits known as ‘little apples of death’ this is a plant to steer well clear of. Found in coastal regions of Florida, South and Central America the manchineel is possibly the world’s most poisonous tree.

Whilst the fruit is said to be potentially lethal if eaten it is the tree itself that poses the greatest threat. Every part is stuffed full of powerful toxins, most notably the sap which contains phorbol, a strong skin irritant. Contact with the sap provokes strong allergic dermatitis resulting in blistering of the skin. This is a particular hazard during rain when anyone taking shelter under the tree’s leaves runs the risk of getting splashed with sap-laden raindrops. Even a tiny amount can cause the skin to blister, not surprising as this stuff can strip paint of parked cars too!
It is also reported that the smoke from burning the wood can cause blindness.

Of course all this potential for pain didn’t go unnoticed. The Carib natives were said to use the sap on their arrow heads, poison the wells of their enemies with the leaves and even tie some unfortunate victims to the trunk of the tree.

7. Suicide Tree (Cerbera odollam)

Suicide tree (Cerbera odollam)

Suicide tree (Cerbera odollam) Photo: Noppharat

With a name like that it is little surprise that this tree is probably responsible for most deaths than any other plant. In the Indian state of Kerala alone it is thought to be responsible for around 50 deaths a year. Despite being called the suicide tree the toxins work equally well for murder and the flavour is easily hidden in a bowl of spicy food.
It is in Madagascar where Cerbera claimed most victims. Referred to as ‘ordeal poison’ it was used in the process of ‘trial by ordeal’. Basically, if you survived you were innocent, if you died you were, well, dead… It is estimated that around 3,000 people a year died in these trials, many willingly submitting themselves to the process believing it infallible. Trial by poison was finally abolished in 1861 by King Radama II.

It is the seed inside the fruit of this plant that is highly poisonous. It contains the powerful alkaloid, cerberin, which is similar to digoxin in foxgloves. These both work by disrupting the heart’s rhythm often with fatal results.
Cerbera odollam is a member of the same family as the previously mentioned  oleander.

6. Deadly nightshade (Atropa belladonna)

Deadly nightshade (Atropa belladonna)

Deadly nightshade (Atropa belladonna)

Like its family members, the potato and the tomato, deadly nightshade contain the glycoalkaloid poison solanine. However, whereas you might have to eat a truck load of tomatoes to poison yourself, a single leaf of belladonna might do the trick for you.

The main toxins in deadly nightshade are  atropine, scopolamine and hyoscyamine all of which effect the nervous system by blocking certain neurotransmitters. Whilst all parts of the plant are toxic, the root is generally most poisonous. A dose of around two to five berries is usually sufficient to kill an adult.
The classic symptoms of poisoning include dilated pupils, blurred vision, dry mouth, hallucinations, loud heart beats (audible several feet away), aggressive behaviour, convulsions, coma and possibly death. The effects of the poison are by no means instant and may take from several hours to days to kick in.

The name Atropa comes from atropine which in turn is from the Greek goddess who cut the threads of life. Belladonna means ‘beautiful lady’ and refers to the 17th century practice of women putting a small extract of deadly nightshade in their eyes to dilate their pupils and make them more attractive.