Plants That Aren’t Good for Human Health!

Many native plants in the United Kingdom are toxic to some degree and this forms part of their survival strategy.

Toxic plant chemicals or phytochemicals protect plants from being eaten, from pathogenic attacks and insect invaders.

Many phytochemicals are contained in all parts of plants, some are mild, some quite toxic and some are downright deadly to man and beast.

Toxicity may only exist in one part of a plant such as the bulb, root or seeds.

In the case of our  most deadly plants every part will contain toxins and is potentially lethal.

These plants have earnt themselves a place in history as the chemical weapons of choice for murderers, executioners, kings and sorcerers alike.

Today not so many people fall victim to these plants, perhaps a couple a year at most. Due to the wonders of modern medicine these plants are now saving far more lives than they have ever taken.

Giant Hogweed (Heracleum mantegazzianum)

This herbaceous perennial belongs to the carrot family or Apiaceae genus and was first introduced to Britain from Central Asia as an ornamental plant in the 19th century. Giant hogweed has made itself very much at home and has naturalised in the wild, being so successful it has now made the invasive species list.

It particularly likes to inhabit riverbanks as its many large seeds like to float down the river much like an invading armada.

Giant Hogweed bud
Giant Hogweed bud. Image Credit: Gordon Brown

Giant is the operative word as this plant can reach five metres in height with thick hollow stems. The huge rhubarb-like flowers earned it the name ‘common rhubarb’ and it displays small white pinkish tinged flowers in umbels.

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The sap is very toxic due to the presence of furocoumarins which are phytochemicals formed as defense for the plant, possibly to protect against a particular fungus that targets giant hogweed.

This chemical is not found in all plants so may only develop when under threat, this explains the rather inconsistent accounts of human reactions to the plant.

If there is a reaction to the furocoumarins found in the sap of the thick stems it can be very nasty requiring hospital treatment in some cases.

Contact with the sap can cause phytophotodermatitis where the combination of sap on the skin and sunlight causes burns and severe blistering.

This reaction can reoccur many years after the initial contact, again initiated by sunlight.

Doctors back in the 1970s asked for the plant to be added to the official dangerous plants list after seeing many children hospitalised with nasty reactions. Children are drawn to the hollow  stems to use as pea shooters.

Giant Hogweed
A spectacular giant species of hogweed, like its smaller cousin the common hogweed but bigger in all respects, growing up to about 2 metres in height. Image Credit: David Dixon

If you come into contact with the sap the best advice is to thoroughly wash the skin, avoid sunlight and seek medical advice. It does resemble other umbelliferous plants and can be confused with common hogweed or cow parsley.

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Despite its reputation giant hogweed does have its fans including umbellifer’s champion Monty Don who fondly recalls playing with it as a child without coming to harm, Monty wrote in the Guardian “it was lovely, big, fun and just there”.

The scientist and naturalist Arthur Erskine Ellis upon finding himself in a forest full of towering plants felt “like Gulliver in Brobdingnag” describing in awe giant hogweed as “this noblest of umbellifers”.

Ragwort (Senecio jacobaea)

The plant has many other names, some are quite rude including ‘Stinking willie’ and ‘marefart’, both referring to the pungent smell of the leaves.

It reaches a height of ninety centimetres, producing yellow daisy-like flowers above tall stems and raggedy leaves from July to late autumn. Nineteen species from the senecio genus are native and found wild in Britain.

Six spot Burnet moth on ragwort
Six spot Burnet moth on ragwort. Image Credit: Kenneth Allen

Ragwort is to say the least, prolific as one plant can produce thousands of seeds. In the Wildlife and Countryside Act (1981) Ragwort is described as “the most dangerous and injurious weed” which when considering some of the other more deadly plants seems somewhat over dramatic.

Its potential to harm livestock is particularly high though due to its prevalence.

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The name comes from its traditional use as a dye, producing vibrant yellow dye from the flowers and green from the leaves.

Ragwort is an unappealing dish with its unpleasant smell and incredibly bitter taste which animals only tend to eat when it’s dry and has lost its flavour. Ragwort is very toxic to horses and cattle but less so to sheep.

Its consumption eventually causes liver damage with the effects being cumulative. Ragwort is toxic to humans, caution is advised when handling it as the toxins can irritate the skin or be absorbed through it.

Ragwort with a cinnabar caterpillar
Ragwort with a cinnabar caterpillar. Image Credit: David Hawgood

Despite being much aligned by landowners, ragwort is very popular with insects, particularly the daisy carpenter bee and cinnabar moth for which it provides an essential source of food. In total ragwort supports around thirty insect species.

Historically ragwort was used by herbalists as a decoction for swellings of the mouth and throat and for treating ulcers.

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The herbalist Culpepper (1616-54) recorded its use for the intriguing “quinsy and king’s evil” and the rather grim “old filthy ulcers in the privities”. Modern herbalist’s may use it externally for wounds and ulcers but it is not recommended for internal use due to its toxicity.

Yew (Taxus baccata)

English yew is one of the longest living native European species, reaching twenty metres in height and forming an impressive tree often with intertwined trunks .Yew is an evergreen with needle-like leaves upon branches that often form a complete canopy.

It is a dioecious plant meaning the male and female reproductive organs exist on separate plants. These male and female parts flower from March to April followed by the red berry like fruit or aril.

Stow-on-The-Wold: St Edward's Parish Church
Stow-on-The-Wold: St Edward’s Parish Church. A pair of ancient yew trees guard the North door of St Edward’s Parish Church.

All parts of yew are toxic including the berries, although not the berry itself but the seed within. Yew is toxic to humans and livestock but the fruit can be eaten by birds and badgers who pass the seed safely.

Yews provide protection and nesting sites in their dense and protective foliage which keeps out the elements. 


Yews are most commonly found in graveyards with some believing they were planted on the graves of plague victims to purify the corpses of all toxicity. They are a symbol of death and also of immortality due to their resilience and longevity.

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There is a unique relationship between the yew and places of worship as the presence of yew in sacred spaces often predates that of the buildings.

Druids associated yew trees with longevity and rebirth, this is thought to stem from their observations of the drooping branches rooting in the ground to form new shoots.

The Celts, and later Chrisitans, associated yew with death, most likely due to its toxicity.

People were often buried with yew and the bodies of the dead were rubbed with it. Reputedly yew branches were used as ‘palms’ at Easter.

Julius Caesar

Yew is extremely toxic and one of the first recorded victims was Cativolcus, King of the Eburones (53 BC) who chose to drink yew juice to end his life. Julius Caesar recorded this  event in his account of his conquest of Gaul ‘The Gallic War’.

Ancient yew tree
Ancient yew tree just outside the west door of the church of St Mary in Eastling, this venerable tree is said to be around 2000 years old.

“[Cativolcus] destroyed himself with the juice of the yew-tree,of which there is great abundance in Gaul and Germany”.

The toxicity of yew can be attributed to the two main alkaloids taxine A and taxine B which are present in the bark and seeds.

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Culpepper discusses the manner of poisoning unique to yew-

Deleterious powers seem to act on the nervous system” [and the manner] “differs from opium and all other sleepy poisons for it does not bring on lethargic symptoms, but penetrates and destroys the vital functions”


Many children have fallen foul of its toxicity due to consuming the attractive, strawberry flavoured berries which are believed to be safe once the seed is removed.

As with Cativolcus,  yew has been ingested as a suicide method hence the removal of the trees from asylum grounds. If intervention is quick the poison can be removed with the administration of a strong emetic such as Ipechuana.

Shakespeare made use of yew’s deadly reputation in both Twelfth Night and Macbeth. The third witch in the first act of Macbeth adds yew to the poisonous brew-

Slips of yew, silver’d in the moon’s eclipse”

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The seventeenth century botanist Robert Turner (Botanologia,1664) discusses yew at some length and proposes a theory on the positioning of yew trees in churchyards, or rather the positioning of churches in relation to the existing trees.

Yew tree berries.
Yew tree berries. Image Credit: Dave Hitchborne


He believed the church should be built to the north or north east of the tree as yews are hot and dry. This is due to the idea the yew tree would trap the gasses released from the church, he writes –

“[yew] will attract poysonous vapours and imbibe them”

These vapours he speaks of are thought to be released by the corpse’s putrefaction and he  names them “will o’ the wisps”.

This led people to believe that if you lay under a yew tree you would imbibe the gasses and die.

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Galen in his herbal of 1579 disputed this idea and claimed he had on more than one occasion slept under a yew and furthermore feasted on berries to no ill effect.

The timber produced by yew is incredibly strong and durable, traditionally used to make long bows. One of the world’s oldest artifacts in existence, being over 450.000 years old, is a yew spear head.

Yew has proved itself both destroyer and life giver.

In today’s modern medicine the drug taxol is derived from the alkaloids taxine A and B taken from the Pacific yew (Taxus brevifolia). This life saving chemotherapeutic agent has treated many previously drug resistant cancers.

Deadly Nightshade (Atropha belladonna)

This perennial is a relative of tobacco and potato, both of which belong to the Solanaceae family. Atropha belladonna is an enticingly beautiful yet dangerous midsummer flowering shrubby plant.

A native of scrub, woodland and banks, preferring areas of disturbed soil, the plant has green leaves and gorgeous purple green flowers followed by the highly toxic black berries which look a little like blackcurrants.

Deadly Nightshade
Attractively sweet and cherry-like fruit of Deadly Nightshade

This psychoactive plant has been considered to be ‘the property of the devil’. The name originates from the latin Atropos who was one of the three ‘Three Fates’ in Greek mythology.

Atropos was responsible for choosing the manner of death of all mortals. Belladonna, meaning beautiful woman in Italian, arises from the cosmetic practice of renaissance women using drops from the plant to dilate their pupils.

The three tropane alkaloids atropine, scopolamine and hyoscyamine give this plant its very powerful toxic effects. It has an anticholinergic action which blocks and inhibits the actions of the neurotransmitter acetylcholine on the nervous system.


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This results in ‘anticholinergic toxic syndrome’ which  begins with hallucinations and agitation progressing eventually to respiratory failure and eventual cardiovascular collapse. A relatively small amount can result in paralysis.

Deadly nightshade demonstrates varying degrees of toxicity from inducing relatively pleasant psychoactive effects to causing death.

In ancient Greece it was used to induce an ecstatic trance-like state in the followers of Dionysus (Bacchus) as an addition to ‘Bacchus wine’. Less pleasantly, deadly nightshade was made into a poisoned paste by the Roman military with which to tip their arrows.

Deadly Nightshade
Deadly Nightshade with abundant flowers and green, immature berries

Witches reputedly concocted a skin potion from bear lard infused with deadly nightshade. This conveyed some toxic effects through the skin resulting in hallucinations where they believed they were flying.


Shakespeare’s heroine Juliet from the tragedy ‘Romeo and Juliet’ takes deadly nightshade to enter a catatonic state and therefore appear dead. Deadly nightshade is known to produce effects that leave a person wavering precariously between sleep and death.

 Culpepper describes Atropha belladonna in his herbal-

This nightshade bears a very bad character as being of a poisonous nature”

The Elizabethan physician John Gerard refers to ‘sleepy nightshade’ to differentiate between the forms-

This kinde of nightshade causeth sleep, troubleth the mind, bringeth madnesse if a few of the berries be inwardly taken, but if moe be given they also kill and bring present death”

Gerard hints that death may be due to misjudgement of dose-

 “It bringeth such as have eaten thereof into a dead sleepe wherein many have died”

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Outwardly deadly nightshade was used as a poultice for inflammatory conditions and was available over the counter during the 1950s in the form of plasters recommended for all manner of conditions.

Deadly nightshade gives us two modern drugs Atropine which reduces secretions and is used during surgery and hyoscine used for motion sickness and spasm in the bowels (buscopan).

Monkshood (Aconitum nappelius)

The native perennial monkshood is a member of the buttercup (ranunculaceae) family and is often grown in garden borders as a striking ornamental specimen.


This is a stunning and showy plant with many flowers borne on tall spikes arising from long stems with feathery leaves.The unusual hood shaped purple blue flowers are beauties as described by Gerard-

 “[flowers]which are so beautiful, that a man would thinke they were of some excellent vertue”.

Monkshood is an extremely poisonous plant that can be absorbed effectively through the skin. Aconite is thought to be a derivative of Akon meaning dart in Greek.

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Monkshood paste was traditionally smeared on weapons and used in the eighteenth century to poison predators, including wolves, giving it the common name ‘Wolfsbane.’

The poison acts on the heart and nervous system beginning with abdominal and chest pains followed by diarrhea, dizziness, nausea and numbness. Eventually it affects the heart and respiratory system resulting in breathlessness and ultimately death.

Monkshood, Aconitum napellus

Poisoning by monkshood was an execution method favoured by the ancient Romans.

Even today monkshood claims an occasional victim, the death of a gardener was reported in 2014, whilst working on a Hampshire estate he happened to touch the plant and died a few days later.

Gerard describes the swiftness in which monkshood acts-

 “an arrowe or other instrument dipped in the juice” kills man or beast “within halfe an hower”

Black Henbane (Hyoscyamus niger)

Not strictly speaking a British native as black henbane was originally introduced from the Mediterranean but has since been found growing wild in many counties on wasteland, roadsides and chalky soil near the sea.

Large flowering henbane

Henbane only tolerates well drained soil and cannot tolerate shade. Either annual or biennial henbane reproduces purely through its seeds of which a single plant can produce half a million during a season. Henbane is a tall plant with tough woody stems and large foul smelling leaves.

The plant produces equally foul smelling flowers which are striking being a pale yellow with deep purple veining and throats.

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Another deadly member of solanaceae is also known as ‘stinking nightshade’. All parts of this are poisonous with the leaves being the most potent. Unpleasant to smell and taste, henbane is not often eaten mistakenly.

The name is thought to arise from fatalities amongst poultry after consuming the seed.

Black henbane was used in ancient times by the likes of the physicians Dioscorides and Pliny for inducing sleep and reducing pain.

Henbane flower
Close-up of the Henbane flower

It was also very important during the Middle Ages having associations with witchcraft, being ritually burnt with inhalation of the smoke inducing hallucinations.

Henbane is similar in action and chemistry to deadly nightshade but its effects are milder, it is still used in modern medicine as an extract using the constituent alkaloid hyoscyamine.This is the chief active chemical responsible for the narcotic action as deduced by the ancient physicians.

Hemlock (Conium maculatum)

Hemlock is a common plant of damp habitats and a tall member of the apiaciea family. It features small white flowers in characteristic umbrella form (umbels) atop thick, hollow stems which are speckled purple (a reliable identifying feature).

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Hemlock has a very repellent smell when the fern like leaves are crushed and this is thought to be the reason that there haven’t been a huge amount of deaths recorded from ingestion of this plant – that combined with the very nasty taste.

Flowers of Hemlock. Image Credit: Robin Stott 

Hemlock was used for executions in ancient Greece and was the method of death chosen by Socrates in 399 BC who relayed his symptoms as the poison took hold, describing the effects starting with a creeping numbness in his toes and fingers until finally reaching his heart.

Hemlock was used by Arab and Greek physicians. The Anglo-Saxons also made use of hemlock and the name has its origins in the Anglo-Saxon language, hem – meaning border or shore, and leac- meaning leek or plant.

The main active alkaloid found in hemlock is conium whichis sedative and antispasmodic.

Foxglove (Digitalis purpurea)

Another deadly beauty found wild on heath and in woodlands favouring the acidic soil is the wonderful foxglove, found flowering from June through to autumn.

These tall showy plants display stalks of beautiful bell shaped flowers which are widely cultivated in gardens.

Foxglove is a very valuable bee plant as the tubular flowers enable long tongue bees to access the pollen.

There are a number of different theories on the etymology of the name ‘foxglove’ including suggestions it relates to fairy folk and is a derivative of ‘folks glove’.

Credit: Albert Bridge

Some connect the name directly with foxes and the Anglo-Saxon term ‘gleow’ which means music. Digitalis is from Latin and refers to fingers, giving us ‘purple fingers’.

Another connection suggests the name is associated with the roman goddess Flora and her vixen familiar.

Ingestion of the plant can cause nausea, headache and diarrhea, ultimately progressing to heart and kidney damage if untreated.

Digoxin is a drug obtained from the dried leaves of foxglove.

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It was one of the first medicines used in cardiology having first been isolated in 1930. Foxglove contains cardiac glycosides which are used to treat heart failure by strengthening the heart’s contractions. Foxglove was first prescribed for oedema (water retention) by the physician and botanist William Withering (1741-99).

Lily of the Valley (Convallaria majalis)

Lily of the valley has oval leaves surrounding exquisitely pretty white flowers in spring followed by highly poisonous red berries.

The flowers exude the most delicate and lovely sweet scent which has been harnessed by perfumers including Dior, the scent being characteristically fresh and floral with a hint of exotic jasmine.

Lily of the Valley
Convallaria majalis, Lily of the Valley. Not a lily as such as the plant spreads by rhyzomes rather than bulbs. The plants usually flower in early May. Image Credit: Jonathan Billinger

This member of the asparagus family asparagaceae can be found on dry chalky soil commonly in woodland and is an ancient woodland indicator.

Lily of the valley has some lovely folklore associations with fairies and the elusive nightingale which is said to be drawn to the sweet fragrance.

The flowers have a perfect miniature quality to them as if too small for a human landscape, appearing to be more suited to forgotten fairy realms.

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This beautiful flower was a favourite of our late Queen, a regular addition to floral displays at Buckingham Palace, and also featured in Kate Middleton’s bridal bouquet. Lily of the valley is also the national flower of Finland.

Another herb indicated for heart troubles, lily of the valley contains cardiac glycosides, the principal one being convallatoxin.

Lily of the Valley.
Lily of the Valley. Beautiful pearls of springtime. Image Credit: Jonathan Billinger

Lily of the valley featured recently in US hit ‘Breaking Bad’ used by Walter White to poison an adversary.

Convallatoxin was used during the Great War to treat victims of gassing who sustained cardiac damage and is still used today in herbal medicine  for congestive heart failure.

Gerard writes here about treating stroke victims with lily of the valley wine-

The floures of the valley lillie distilled with wine and drunk the quantity of a spoonefull, restore speech unto those that have the dumb palsie and are faine into the apoplexie”

Lords and Ladies (Arum maculatum)

Commonly known as cuckoo pint, this member of the araceae family has distinctive large arrow shaped leaves and produces tiny yellow or purple flowers. These insignificant blooms emerge early in spring borne on a spike called a spadix.

The spadix rises somewhat ominously from a green cobra like hood forming a glossy backdrop which highlights this strange protrusion. The flowers are followed by striking dark orange to red berries in autumn clustered around the spadix.

Lords and ladies
Lords and ladies. Credit: Albert Bridge

This interesting little plant can be found growing in shady hedgerows, along riverbanks and in woodland.

The name lords and ladies seems to refer to the appearance of both male and female flowers on the same plant. The flower stem or spadix is either purplish if male ‘lords’, and the female flowers ‘ladies’ cream coloured. 

A ring of hair above the male flowers traps insects allowing them to become dusted with pollen which is then carried to the female flowers of other plants. The bright berries form after the female flowers and are incredibly toxic.


The folk name ‘cuckoo pint’ arises from the plant’s emergence in early spring when the first cuckoo can be heard, added to this is a derivative of the slang term ‘pintle’ meaning penis and referring to the phallic shaped spadix.

Berries of Lords and ladies
Berries of Lords and ladies. Credit: Albert Bridge

The vibrant berries contains oxalate crystals which can penetrate skin and cause irritation.

If these happen to be consumed they can cause throat swelling leading to breathing difficulty and potential death.

It is unlikely one would consume a fatal dose as the unpleasant reactions begin as soon as the berries are placed in the mouth and the taste is acrid.

The peaceful beauty of the English countryside can belie the powerful and dangerous chemicals that many plants quietly harbor in the shade of protective woodlands or along pretty riverbanks.

It is indeed a very sensible practice to teach children about how to identify and avoid dangerous plants in the wild.

We can educate through the telling of stories concerning the misadventures of our ancestors and avoid adding to this archive of malevolence and mishap.

The power of plants is truly awesome and how we have learnt to harness their toxicity to reduce our suffering really is a tonic to the heart.

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