Activities and Disciplines

Poisonous Plants and Fungi

Do you know which plants and fungi are poisonous?

The brown hay cap Panaeolina foenisecii is a common mushroom that grows in short grass, such as on lawns. It accounts for most childhood cases of suspected poisoning by fungi, but only causes symptoms if large numbers are eaten.

We can all name a few poisonous plants, and possibly even identify them, but the majority will come as a surprise. Perfectly ‘safe’ plants may be wrongly considered poisonous; particularly if your child has just eaten some. As for ‘mushrooms’ and ‘toadstools’: what is the difference? There is room for us all to increase our knowledge of which plants and fungi are poisonous.

Staff of the Guy’s & St Thomas’ Poisons Unit collaborate with the Royal Botanic Gardens, Kew, to find new ways to help. The Poisons Unit handles emergency poisoning enquiries from doctors and nurses in the south-east of England. They know how important it is for plants and fungi to be identified correctly so that the right treatment can be given.

Identification

Several plants have the common name nightshade. Deadly nightshade Atropa belladonna has black fruits that have be mistaken for bilberries although they are much larger. The fruits of the more common woody nightshade turn from green, through orange, to red. Both are poisonous.

In 2000, we published an interactive identification system on CD-ROM: Poisonous Plants and Fungi in Britain and Ireland. It is used by many Accident & Emergency Departments in hospitals around the country, as well as by parents, local authorities, and other interested people. By answering simple questions about the plant or fungus you can make an accurate identification, confirmed by a comprehensive set of photographs. Detailed information about the toxicity of the plant or fungus can then be read and printed, including: poisonous parts; toxins (poisonous chemicals); symptoms; and treatment advice.

Buying a Plant

Many houseplants, such as dumb cane Dieffenbachia belong to the Araceae family and contain calcium oxalate crystals. When chewed, these damage the mouth and throat causing a burning sensation and swelling of the soft tissue. Young children and pets are particularly at risk.

When you go to your local garden centre to choose plants for your house or garden, look carefully at the labels. As well as telling you things like the name of the plant, how big it will grow, how much sun it likes, you will also see a warning if the plant is poisonous. For example, labels for the common houseplant, Dumb Cane (Dieffenbachia) should say CAUTION toxic if eaten/ skin and eye irritant. Kew and the Poisons Unit compiled detailed reports on the toxicity of cultivated plants and worked with the Horticultural Trades Association to produce a list of plants that should carry warnings.

Children

The largest group of people at risk from poisonous plants is children under the age of 5. They spend time in homes, gardens, parks, and the countryside with their parents and child-care providers such as childminders, nurseries and grandparents. Our next challenge is to produce an information guide that can be used by all these people to keep children safe. It will provide images and brief information to enable poisonous plants to be identified. Based on our previous work, we are in the best position to: outline which plants pose a potential risk; help people to work out the degree of risk; and suggest steps to avoid harm. This guide is currently being compiled.

Skin reactions

Handling some plants can result in a severe skin reaction. German primula Primula obconica causes an allergic reaction in sensitised people, but allergen-free cultivars have been developed in recent years. Other plants, such as giant hogweed Heracleum mantegazzianum and garden rue Ruta graveolens, cause a phototoxic reaction. Irritation, pain and blisters result from exposure to plant sap in bright sunlight.

Resources

• Enquiry service Cases of suspected poisoning, and questions about the toxicity of plants, are routinely handled by the enquiry service at Kew.

• Books and a CD-ROM are available from Kew's online bookshop. Currently available:
  • CR-ROM - Poisonous Plants and Fungi in Britain and Ireland
  • Book - Poisonous Plants and Fungi: An Illustrated Guide
  
  
• Reading list on poisonous plants.

• The Royal Horticultural Society has an excellent pamphlet on poisonous plants, for free download.

Acknowledgements

The work on poisonous plants and fungi undertaken jointly by Kew and the Guy’s & St Thomas’ Poisons Unit has been made possible by donations and grants. The generous support of the following organisations is gratefully acknowledged:

• Special Trustees of Guy’s Hospital;
• British Library;
• Children Nationwide;
• Kirby Laing Foundation;
• Trustees of the Royal Botanic Gardens, Kew.

Contact details

If you would like to support this work, and for further information, please contact:

Dr Elizabeth A. Dauncey, Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB

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