A guide to some of the world’s most poisonous plants

• Written by Holly Hughes on February 16, 2022

You would never think to look at some of the stunning plants and flowers out in nature that they could be anything other than beautiful. That, beneath their divine petals or the dramatic orientation of their leaves, they could hold a poison deadly enough to kill someone.

And yet, beautiful but dangerous flowers exist. Turns out that there are many dangerous plants for humans, animals, and insects out there. Let’s look at some of the most common toxic plants – and some of the most deadly flowers.

Most common poisonous plants

Almost anywhere you go, you are sure to find a seemingly innocent plant that actually has a much darker side to it. There are different kinds of poison plants to be found in every corner of the world, many of them appearing as weeds. Here’s a list of some of the most common of them.

Lantana

Abundant in the tropics, lantana is a very common flower that is often treated as a weed in many countries. Despite the allure of its intense fragrance and brightly-colored flowers in yellow, red, violet and orange tones, lantana is highly poisonous as every part of the plant is filled with liver toxin. Fatigue, vomiting, depression, and liver failure are all possible symptoms if ingested.

Foxgloves

In every list of poisonous flowers, you will find foxgloves front and center. Despite being used in several medicines, all parts of this plant are still poisonous and can cause stomach pain, fainting and headaches. They are particularly harmful to animals.

Calotropis

If you’ve ever been to South Asia, you probably know about one of its most common weeds – Calotropis. This plant contains calotropin in the latex that seeps from its flowers and leaves and, if this makes contact with the eyes, can cause blindness.

Paralyzing plants

So those are some common poisonous plants which, though with painful side effects, are often mild or at least treatable if ingested. However, not all plants are so forgiving. Here’s a couple of plants that have the potential to cause paralysis, asphyxia and even death!

Gelsemium

All three varieties of this plant have the potential to be deadly. The most toxic variety – known as Gelsemium elegans – is grown in Asia and referred to as “heartbreak grass”.

This is because, if the dose is big enough, Gelsemium elegans paralyzes the spinal cord which in turn causes an almost total loss of any muscle power. This usually results in asphyxia.

Aconitum - the devil’s helmet

Popular in witches’ love and flying potions during the Middle Ages, the devil’s helmet, which is a member of the buttercup family, earned another title from its lethality: the Mourning Widow. This is because, when used in love potions, its poison would often end up killing a beloved’s intended. A mere few drops from Aconitum roots is enough to paralyze a person’s cardiac muscles or entire respiratory system, resulting in certain death.

So watch out any lovers out there!

The world’s most dangerous plants

Now we’ve seen how lethal some plants can be, there’s only one question that remains - of all the most poisonous plants, which is the deadliest of them all?

Castor Oil Plant

According to the Guinness Book of Records, the world’s most poisonous plant is the castor oil plant. Just one milligram of ricin, the plant’s poison, is enough to kill a human adult according to the Centers for Disease Control (CDC).

Oleander

One of the most toxic plants in the world is oleander – made even more dangerous by the fact it is so beautiful. Fragrant, colorful, and charming, oleanders are beloved for their beauty however they are highly toxic and a particular hazard to children. Nerium oleander, for example, is toxic from its sap to its stem and even burning oleander can cause poisoning.

This plant can even be fatal, with other symptoms of poisoning including fever, slow heartbeat, dehydration, and tremors.

Common toxic herbs

Finally, while we often associate herbs with health, cooking, and medicine, even some herbal plants can be poisonous. Common toxic herbs include sassafras which can cause liver damage, hallucinations, trembling, shock, and even has the potential to cause cancer.

Borage is a skin irritant while Calamus also causes skin irritation as well as upset stomach and cancer. Liver damage is common if Chaparral or Comfrey is ingested.

Frequently asked questions about toxic plants

Which plant holds the Guinness book of world records’ title for world’s most poisonous plant?

The Castor oil plant holds the record for being the most poisonous in the world.

Can lily of the valley kill you?

Yes, lily of the valley has the potential to be fatal if ingested, particularly to children. Lily of the valley is a “1” on the poison scale, meaning it has extreme toxicity that can lead to death.

Are petunias poisonous to humans?

Petunias are not considered toxic if using a non-GM variety.  

What flowers have cyanide?

Hydrangeas contain a small amount of cyanide. If heavily ingested, this can be lethal.

Will my dog eat foxglove?

Foxglove is highly poisonous so dogs or indeed, any animal, should not eat it under any circumstances.