Do you like to spend time in the garden with your children or with pets? Do you like have vases with flowers to enliven your living areas? If so, it is wise to be sure that you know which plants could be dangerous.
Plants evolved over millions of years with other living creatures. This association has resulted in plants developing defences for their survival that include poisons in plant parts that help resist damage from creatures that would feed on them. This protects the plant and allows normal growth, flowering and seeding to occur so that it can reproduce itself. While these poisonous qualities are good for plants, they are not so good for us if we are not aware of which plants are dangerous and know how to handle them appropriately.
What Makes Plants Poisonous?
Many plants contain alkaloids – organic compounds containing nitrogen. There have been approximately 3000 found in some 4000 plant species, often synthesised in leaves. They do not seem to have any important metabolic function but an ecological function, being toxic to browsing, grazing animals and leaf eating insects. The first to be isolated was morphine, found over 150 years ago in the Opium Poppy (Papaver somniferum).
Many plants have oils, latex or sap that contains poisons. Some can cause mild to serious skin irritation causing itching or blistering if handled, but most are dangerous only if ingested or swallowed causing symptoms similar to food poisoning. A few can cause serious purging, delirium and death.
Some plant poisons can be inhaled from smoke or pollen and spores. Poisons affecting the eyes may begin with irritation, pain and even blindness.
Other plants have sharp thorns or irritating hairs that damage skin causing pain and leading to infection. Such plants are more dangerous as they age and increase in size.
Where Do You Find Them?
Humans have been managing plant growth to suit themselves for thousands of years and have been able to select and cultivate the most edible, avoiding dangerous poisonous plants (sometimes after fatal tasting results). But humans also enjoy the presence of all kinds of ornamental plants around them and the horticultural industry thrives on providing plants for this purpose.
There are a few indigenous poisonous plants found growing naturally but most poisonous plants are exotic species found in home or public gardens or as weeds. These may be in flower or fruit for many months. Flowering may be from mid-winter through to summer with fruit generally from late spring to autumn. Evergreen species are always in leaf. Children are most likely to “experiment” with plants by tasting them.
What Are Some Common Poisonous Plants? (not an exhaustive list)
Bulbs and similar plants
Amaryllis – Belladonna Lily
The sap can cause skin irritation and if ingested causes violent purging and could be fatal.
Narcissus – Daffodils and Jonquils
All Narcissus are toxic. They have been mistaken for onions.
Agapanthus africanus and other species
The succulent leaves and the bulb of Agapanthus are toxic and cause skin irritation and mouth ulcerations.
Alocasia, Arum, Colocasia, Zantedeschia species – Arum Lilies
All are dangerously poisonous. Sap causing severe swelling on contact with the throat or mouth. Some have caused death.
Hyacinthus – Hyacinth
These are well known in gardens but contain very toxic substances. Avoid growing them indoors and if storing, label and separate them from other bulbs.
Convallaria – Lily of the Valley
A creeping lily with small, highly perfumed, white bell shaped flowers. The leaves and berries are very poisonous causing nausea, headaches and in extreme cases heart failure.
Herbs and small shrubs
Vinca major -Blue Periwinkle
A garden plant that has been become an environmental weed. It contains at least seven alkaloids including vincamine which affects blood circulation in the brain.
Aquilegia – Columbine
All parts of the plant contain cyanogenic glycosides and the seeds contain hydrocyanic acid. There are records of death caused by consumption of the flowers.
Anemone – Wind Flower
A common garden plant. All parts including roots, flowers, leaves contain poisons that are dangerous if swallowed.
Cheiranthus – Wallflower
These are poisonous in all parts, but especially the seed. They contain a crystalline alkaloid that acts on the nervous system.
Delphinium and Larkspur
All species are poisonous and the seeds in particular. Care should be taken when handling and cultivating the plants.
Digitalis – Foxglove
All species have some degree of toxicity. Children can die from consuming small amounts. Symptoms are nausea, breathing difficulties and pulse irregularities.
Echium – Vipers Bugloss, Paterson’s Curse, Pride of Madiera
The leaves and flowers contain poison that causes liver failure.
Helleborus – Hellebore, Christmas Rose
All species contain some level of powerful cardiac poisons that can cause heart failure.
Lathyrus – Sweet Pea
Human poisoning is usually caused by eating the seeds. The symptoms are a slow pulse, respiratory irregularities, depression and paralysis. Don’t mistake them for edible peas Pisum.
Papaver – Poppies
Both the leaves and flowers are toxic. Poisoning causes increased respiration rate, followed by coma, though fatalities are rare.
Some species contain serious poisons. They can cause dermatitis and other skin irritations.
Rheum – Rhubarb
The leaves are very poisonous causing nausea and vomiting and can be fatal. The edible stems have quantities of potassium oxalate and sufferers of rheumatic or kidney problems should avoid excessive intake.
Shrubs and Trees
Buddleia – Butterfly Bush
A tall shrub with long spikes of perfumed flowers in summer. A weed in some mountain areas. The plants contain chemicals that make them potentially dangerous.
Brunfelsia – Yesterday, Today, Tomorrow Bush
Evergreen shrubs with fragrant flowers. The leaves and fruits are highly toxic. The berries have been known to poison dogs causing fever, vomiting, muscle tremors and seizures.
Buxus – Common Boxwood
A slow growing shrub often used for hedging. The foliage contains a poison known to be fatal to stock and is potentially dangerous to humans.
Berberis (Mahonia) – Barberry
There are many species. They generally have sharp thorns and their usually yellow flowers are followed by berries that are slightly to very poisonous.
Cassia (Senna) Silver Cassia, Buttercup Bush, Spartina, Genista, Teline, Broom
These are shrubs and tropical trees. The foliage and seeds are poisonous causing severe purging and pain if swallowed.
A small tree with yellow flowers in spring. Both the flowers and seed have toxic properties.
Cotoneaster – Clusterberry
The berries of most species causes some degree of poisoning and gastroenteritis if eaten.
Hydrangea – Hydrangea
The leaves contain chemicals that cause symptoms similar to cyanide poisoning with human poisoning on record. The plants are known to harm stock.
Veronica, Hebe – Speedwell
There are about 250 species with a few native to Australia. Hebe is from New Zealand. All have some degree of toxicity.
The fruit is very toxic and symptoms of poisoning include the burning of the mouth and stomach and purging before collapse.
Kalmia latifolia – Calico Bush, Mountain Laurel
This fairly common flowering shrub contains toxic chemicals.
Euphorbia – Spurge, Milkweed, Poinsettia
The caustic milky sap can cause burning of the skin, blindness, and if swallowed purging, delirium and possibly death.
Rhododendron – Rhododendrons and Azaleas
All parts can be fatal if ingested. Produces nausea and vomiting, depression, difficult breathing, prostration and coma.
Rhus succadania – Sumach, Wax Tree, Varnish Tree
Rhus cotinus (Cotinus coggygria) – Smoke Tree,
These are commonly found in Melbourne gardens. The sap is extremely poisonous and can cause severe dermal poisoning or similar skin reaction. Australian hospitals regularly record poisoning from these plants each year.
Nerium – Oleander
Poisoning has occurred from inhaling the smoke of the burning wood and people have been known to die after using sticks as meat skewers. Leaves and flowers are poisonous.
Brugmansia or Datura – Angel’s Trumpet
Poisoning is not uncommon in humans and animals. The symptoms include delirium, raised temperature, intense thirst, convulsions before coma and death.
Have bitter acids and tannins in their bark. Clusters of white, usually fragrant flowers followed by black succulent berries that are poisonous.
Eucalyptus – Gum Trees
All species contain oils that are toxic if ingested. Severe cases can cause delirium, convulsions and death from respiratory paralysis. Even a few drops of oil from the leaves of E. globulus – the Tasmanian Blue Gum are poisonous.
Prunus – Peaches, Plums, Apricots, Cherries
The kernels of these edible fruits contain chemicals that produce a bitter taste. The kernels of the Cherry Laurel (Prunus laurocerasus ) is particularly dangerous. Peach leaves are quite poisonous.
Ipomoea, Convolulvus, Calystegia – Morning Glory, Noon Flower
About 500 species with about 40 in Australia. They cause hallucinations and liver damage.
Lonicera – Honeysuckle
The leaves of some contain poisonous alkaloids. The seeds of all are dangerous.
Often house plants. Animals eating the leaves suffer violent twitching before collapse and death. The poison damages the liver and intestines.
Hedera – English Ivy
The leaves and berries are poisonous causing skin allergies, nervous disorders, convulsions and internal damage including diarrhoea.
Many are highly poisonous, typically mushroom like. Some are highly colored, others a smooth grey. Poisoning causes profuse salivation, with severe gastrointestinal pain and complications. These effects can be delayed some hours after ingestion. Severe cases can lead to coma and death.
We have not been able to cover all poisonous plants, but for some more, particularly flowers see https://blog.flowersacrosssydney.com.au/most-dangerous-plants-flowers/
The highest number of poisonings from plants is from fungi.
Don’t eat fungi unless you are very sure that it is an edible species.
Be aware and take care in the garden and bush
For poisoning cases contact the Poisons Information Centre on 13 11 26
McKenzie R. 2012. Australia’s Poisonous Plants, Fungi and Cyanobacteria – A Guide to Species of Medical and Veterinary Importance. C.S.I.R.O.
Everist SL. 1981. Poisonous Plants of Australia Revised ed, Angus and Robertson, Sydney.
Australian National Botanic gardens. 2015. Poison Plants