Beware this Halloween: Poisonous plants that may be growing near you

Autumn Crocus Flower

Fiann Ó Nualláin gives a Halloween countdown of the world’s top poisonous plants which may be growing in a flower bed near you.

Scarier than fireworks, and more ghoulish than you may have suspected, the five deadliest plants on the planet could be outside your front door now. Let the countdown commence...

Number 5: Hemlock

Conium maculatum is in the same family as parsnip, fennel and carrot. It looks just like like cow parsley and could be mistakenly planted as an ornamental. Foragers should note it has been fatally mistaken in the past for escaped caraway or self-seeded parsley.

Hemlock was part of the brew that made up the poison chalice of ancient Greece — utilised as a means of execution for prisoners and trouble makers. It ended the life of the philosopher Socrates and also, his research into the nature of reality and truth.

The foliage, seeds and roots are packed with a potent alkaloid toxin known as coniine – which kills by what is known as “ascending muscular paralysis”. Your toes go numb, and then you can’t feel your lower legs, then your thighs freeze and so on up the body until it stops the action of your respiratory muscles and grips your throat.

Curiously enough, it has a herbalistic history in treating asthma and other respiratory conditions — definably not one to try at home. The generic name Conium derives from the Greek Konas, meaning to spin about — vertigo being the least of its side effects — but its specific name ‘maculatum’ meaning ‘spotted’ (the purple marks on its stems) allude also to the mark of Cain, it was said, and thus its murderous action.

Folkloric antidotes include tannic acid, stimulants and coffee — it’s a serious emergency so don’t go messing about making a cup of coffee — phone an ambulance and maintain airway as best as possible.

Number 4: Foxgloves

Digitalis purpurea, aka witches’ thimbles; aka dead men’s bells; aka dead man’s fingers, contain many powerful toxic compounds but three that justify those AKAs include Deslanoside, Digitoxin and Digitalis glycoside.

All three impact on the heart — the cardiac drug digitalis came for early herbal uses of the plant and scientific experimentation in the 1700s — again not one for self-medication as minute doses are potently harmful.

A beautiful ornamental for any garden, be aware that the entire plant is toxic, leaves, roots, sap, flowers, seeds, and even inhaling the pollen can react badly with more sensitive gardeners. Ingestion can be fatal – even from just a leaf or two.

It kills by slowing the heart so much that it struggles to supply enough oxygen to the brain and so the brain suddenly forces it to ‘emergency pump’ at rapid rate thus causing a massive heart attack. Hive reactions to touch alone are known and bad hallucinations to pollen can occur – it is believed it was one of the many plants utilised in the original ‘witches brew’ — the one that helped them ‘fly’ — but the safe recipe for that went up in flames at the stake too.

Foxglove is also toxic to animals — that includes livestock and pets. The blotches on the throats of the flower echo the dead man’s finger common name and again, the murderous mark of Cain.

Antidotes include activated charcoal and laxatives but again I recommend you visit an emergency room via ambulance.

Number 3: Monkshood

Aconitum, aka wolfsbane; aka devil’s helmet, is a plant long utilised throughout human history and prehistory to concoct poison-tipped arrows for hunting and warfare — hence it being the bane of wolves.

The ‘helmet’ and ‘hood’ refer to the unique and exquisite flower heads, but also remind us of a time when the only occasions you would see a monk outside of cloisters was as a medicinal practitioner, (to hopefully cure your ills), or to pray over a grave (failure to cure those ills).

Indeed the plant is somewhat grave, having many toxic alkaloids that include neurotoxins and cardiotoxic principles — it kills by first disrupting gastrointestinal function and slowing motor function, finally triggering lung and heart paralysis.

The generic name comes from the ancient Greek ‘akóniton’ meaning ‘without struggle’ – that’s how effective a poison it was — no effort required and an inevitable outcome.

Death usually occurs within one to six hours of fatal dose but you don’t necessarily go quietly — with stomach burning, face tingling and asphyxia often accompanying the process. The devil of it is that you don’t even have to ingest the poison — its aconitine toxin is absorbed easily through the skin so poisoning can occur by just picking the leaves or cutting back without wearing gloves.

It is one of those poisons that crop up on all those TV shows where the wife is not clever enough for the forensic team investigating her husband’s untimely death. A tale as old as time, perhaps, in Greek mythology Medea tried to see Theseus off with a cup of monkshood tea. Don’t try it at home— couples counselling and divorce are simple procedures nowadays.

Number 2: Naked ladies

Colchicum autumnale, aka autumn crocus; aka meadow saffron. Normally naked ladies don’t make me run, but these femme fatales are true deadly beauties — they contain the highly toxic principles of colchicine and colchiceine which, upon ingestion deliver death within 24 hours.

Gastrointestinal symptoms escalate within a 24hr period to convulsions and blood clots that contribute to multi-organ failure and myocardial infarction — a full on heart attack. In some instances ascending paralysis also occurs.

The horror here is there is no delirium — just a slow, agonising death while fully conscious to the end. It’s a very distinctive plant, but people continue to mistake it for saffron (understandable as it’s crocus-like). It’s also dug up as wild garlic, which apart from being in different seasons, it looks nothing like, smells and tastes less like – so if you are going to forage you will need pictures from that book/website/course material and not just botanical descriptions.

If you’re not 100% sure, move on or go trick or treating. There is no specific antidote but treatments exist. Get to a hospital. Don’t panic if you are on Colchicine via prescription as a treatment for gout – its safe in standardised dosage.

Number 1: Castor Oil plant:

Ricinus communis — I grow this for its stunning beauty, the red tones of its flowers and foliage are exquisite. I use castor oil which comes from it, in many of the herbal preparations I make, but I never press the seeds myself — I buy the castor oil.

The fact that it is considered the world’s most poisonous plant is due to its seeds. You’ll have heard of terrorist attacks in the past using Ricin and I am sure any future bulletins on bio-terrorism will reference it — well, that deadly toxin comes from ricinus seeds.

Its murderous potential has cropped up several times on the hit TV show Breaking Bad. The generic name is from a combination of the Latin words ‘Ri’ meaning ‘thing’ and ‘cinus’, denoting ‘destruction’ or ‘ruin’. So it is a plant that brings destruction and ruin — it does that in a disturbing way too. Ingestion of the seeds may initially burn the mouth and throat but progression is to intense abdominal pain and eventually bloody diarrhoea. If untreated death usually occurs within 2-5 days. The good news is that the beans are highly emetic so you may just throw up the deadly agents before they do you harm.

The crushed seeds however, secrete a residue that is potent — ‘ricin’ — a simple protein that if inhaled or ingested inhibits human cellular metabolism and leads to death.

There is no civilian antidote (both the British and US military have unapproved trial antidotes), and so treatment relies on symptomatic support including kidney dialysis and heart-lung machines.

All that being said — nature is glorious and all these plants are beautiful in their natural habitats and even in your garden. Just keep them out of your mouth and off your skin — stick with the toffee apples instead.

Fiann O’Nualláin is botanist, garden designer, commentator and author of The Holistic Gardener, available in bookshops and online


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