Plato contains information on 200 plants or plant groups It even allows for some mistakes non-botanists are likely to make
A computer program is helping doctors to identify lethal species. Rob Stepney reports It is late evening in the information room of the National Poisons Unit in London. A casualty officer rings from a hospital in the north of the country. He has a child with nausea, abdominal pain and a raised heart rate who three hours ago "ate some red berries". A three-inch twig has been brought to the hospital, but doctors cannot identify it. Can anyone help?

The call is typical. It is one of almost 5,000 queries about suspected plant poisoning (mostly in the under five-year-olds) that the unit's round-the-clock service deals with every year. Based in south-east London, its poisons information centre, the busiest in Europe, is stacked from floor to ceiling with works of reference.

"Without being sure of the plant concerned, it's terribly difficult to give treatment advice on the phone," says Dr Virginia Murray, a consultant toxicologist with the unit who is dealing with the call about the boy who ate the berries.

"The berries could be Cotoneaster or hawthorn, both of which are essentially harmless. Or they could be one of the nightshade family, which are potentially highly toxic. There is simply no way of knowing for sure."

Most cases of plant poisoning are in children who are quickly taken to hospital, so severe symptoms are avoided and few deaths result. There is an average of three fatalities a year, and these tend to be of adults who have eaten plants they have misidentified. "In separate cases in 1993, two people died after eating the tubers of the hemlock water dropwort, which they probably mistook for wild parsnip," Dr Murray recalls.

Emergency department staff will usually play safe and admit the child for observation, with all the anxiety, expense and dislocation of family life which that entails. The child may also receive unnecessary treatment. Contrary to popular belief, stomach washouts are not routine, but drugs may be used to induce vomiting. Patients can also be given activated charcoal, which absorbs toxins, in the form of an unpleasant slurry drink.

To overcome the frustration of not knowing exactly what they are dealing with, doctors at the National Poisons Unit have collaborated with a team from Kew Gardens to produce the world's first interactive, computerised system of plant identification. The fruit of four years' work, the Plato (plant toxins) program is still undergoing final trials at selected hospitals in the south-east. But Dr Murray and the botanist Christine Leon, who have been the driving force behind Plato, hope that casualty departments all over the country will soon be able to use it on their desktop computers.

Plato contains information on 200 plants or plant groups (covering several thousand species). Suspects can be identified from their seeds, fruits, leaves or bulbs by answering a series of simple, multiple-choice questions designed to lead the botanicallyunsophisticated through the jungle of classification.

The software is so user-friendly, Christine Leon claims, that it has a built-in allowance for the mistakes non-botanists are most likely to make. The cleverness of the system has just been acknowledged by the award of one of the three British Computer Society "Oscars" for information technology.

To put Plato through its paces, I was asked to identify a mottled brown seed the size of a large baked bean. All that I knew for sure was that it came from a garden plant. By answering questions about its size, symmetry, shape and colouring, Plato led meto the right answer in less than 10 minutes. One reason for the speed is flexibility: the computer works out which question to ask next based on the answer to the previous one, so minimising the number of steps needed to reach a conclusion.

Once I had the likely suspect, I could confirm its identity by calling up coloured photographs of the seed itself, and of the plant's leaves and flowers. Also provided is the formal botanical name, and data on toxicity. It is at that point that a doctor would call the poisons unit for definitive advice on treatment.

The seed I was given turned out to be that of the castor oil plant, Ricinus communis, which contains the potentially fatal substance ricin. So it is surprising to find that the same seeds are still easily obtained through mail-order plant catalogues and from many garden centres. The packet I was shown had the warning "Poison" stamped on it. But there is no legal requirement for this to be done.

The only pressure for toxic plants to be sold with appropriate warnings comes from a voluntary code of practice introduced last September by the Horticultural Trades Association. The National Poisons Unit and Kew Gardens provided the scientific and medical information on which the code is based.

"The work involved in producing new labels as crops come up could mean it is several years before the code is fully implemented," says Bob McKinley, adviser to the association. "But most retailers seem reasonably happy with it."

Whatever the commercial concerns, it is likely that garden centres will be given only limited time to put their houseplants in order. Nigel Smart, a trading standards officer with Oxfordshire County Council, speaks plainly on the point. "Since it is an offence for anyone to sell dangerous products, trading standards officers have a legitimate interest in potentially toxic plants," he says.

However effective the point-of-sale labelling of plants and seeds, we will continue to encounter a great range of vegetation which has the power to injure the unwary. In an effort to increase general awareness, the poisons unit and Health First, the health promotion agency, are launching a poster campaign this week. Each of the three posters (for home, garden and countryside) covers 10 plants, chosen on the basis of their toxicity or the frequency with which they cause concern.

The garden poster features laburnum, monkshood or aconite, autumn crocus and yew, all of which are dangerous when eaten. Also represented are plants that may cause unpleasant skin reactions. These include rue, a herb whose sap causes painful blistering when affected skin is exposed to sunlight, and the spurges, or Euphorbia, which secrete an irritant milky sap. Even experienced plant handlers are not immune to this problem. Recently, two professional gardeners who were pruning spurge in a greenhouse hadto receive medical attention when sap spurted into their eyes.

Wild plants that are harmful if eaten include the woody, black and deadly nightshades, black bryony, wild privet, cherry laurel and lords-and-ladies (all of which have attractive but toxic berries), horse chestnut (chewing conkers is not a good idea) andthe giant hogweed (which causes skin blistering).

Potentially toxic plants found in the home include the umbrella tree and German primula (both cause allergic skin reactions). Angels' trumpets or datura and leopard lily or Dieffenbachia, mistletoe and oleander are all toxic if eaten. Also present on thelist is the daffodil since its sap can cause skin and eye irritation, and its bulbs mistakenly fried or stewed are a frequent cause of vomiting and diarrhoea.

We are likely to be hearing more about poisonous plants. There is an influx of increasingly exotic varieties designed to stimulate a jaded houseplant palate. "Many tropical species have a nasty sap," says Ms Leon. Another factor is evolution. In the caseof the hogweed, there is evidence that the imported giant species is cross-fertisilising with native hogweeds and passing on its skin-blistering properties.

A third reason is increasing awareness of the threats plants may pose. The traders' voluntary code deals only with risks from eating plants or skin contact. But the National Poisons Unit is keeping an eye on plants that may be harmful by inhalation. The weeping fig Ficus benjamina, for example, is suspected of giving off volatile oils that could exacerbate asthma.