End Lines: The map - Field hospital

Plants have always been a prime source for our most powerful medicines. But where, asks Michael Day, do these little miracle cures come from?

This year is the centenary of the first official use of aspirin. Originally prescribed to treat headaches, gout and rheumatic pain, it's now also recommended to fight heart disease and may even prevent bowel cancer. Pretty impressive for a humble painkiller based on extracts from the willow tree and meadowsweet. But aspirin isn't the only important drug derived from plants. Dozens of others have similar origins, and there could be hundreds more waiting to be exploited. If we don't destroy their eco-systems, they may provide breakthrough treatments to transform the next 100 years of medicine.

Mexico The Mexican Yam might not seem a likely agent for one of the great social changes of this century. In the early Forties, however, species native to Central America were found to contain enough of the steroid diosgnenin to make viable the commercial production of oral contraceptives. The vegetable also produces cortisone and hydrocortisone, for treating arthritis and asthma.

Bolivia The mountain forests of Bolivia gave us the first effective treatment for malaria. In the 17th century, missionaries learnt from native Indians that the bark of the cinchona tree cured fevers: from this bark the bitter-tasting quinine was isolated. It's still the main treatment for cerebral malaria, the deadliest form of the disease, in the worst- affected continent, Africa. The disease kills over two million people a year, but without quinine the toll would be much higher.

England One of the oldest heart medicines is found in English country gardens. Digitalis, a mixture of alkaloids from the foxglove (Digitalis purpurea) has been used since the late 18th century to regulate the beat of the heart and strengthen its contraction. Digitalis is no longer used in its original form, but the purified forms of digoxin and digitoxin are currently back in fashion because of their proven ability to keep heart-failure patients out of hospital.

Colombia The coca bush (Erythroxylum coca) is best known for giving the world Colombian marching powder. But we shouldn't forget that cocaine, apart from giving rock stars' sinuses a bit of gyp, has also provided chemists with the chemical blueprint for such compounds as lignocaine, the most widely-employed local anaesthetic. Cocaine was imported into America and Europe as a tonic in the middle of the last century. It was in 1884 that it brought about a revolution in surgery when doctors discovered its power to deaden the nerve endings.

Turkey The opium poppy (Papaver somniferum) has given us a painkiller even more important than aspirin: morphine and its derivatives. Morphine has been used recreationally for thousands of years. Today its legitimate use is restricted to medicine, but our inability to synthesise this alkaloid means we have to rely on opium farming. India, Russia and Turkey supply the above-board stuff, while "The Golden Triangle" on the borders of Laos, Thailand and Burma supplies the black market. Morphine and its close relative diamorphine, better known as heroin, have recently undergone a renaissance in medical circles, with experts stressing that side-effects such as addiction have been overplayed to the detriment of their remarkable ability to ease pain.

Mozambique Tapioca, scourge of school dinners, may help us find a drug for cancer. Cassava, the source of tapioca, stores cyanide. (In the last decade, 10,000 people have been paralysed by improperly prepared cassava in Mozambique, Tanzania and Zaire.) Tests are underway to see if the cyanide-producing enzyme can be targeted at tumours in the body.

China In South-east Asia the falciparum parasite that causes deadly cerebral malaria is becoming resistant to quinine (see Bolivia). If, as expected, the resistant strain spreads to sub-Saharan Africa, the results could be catastrophic. Just as well then that there is an alternative Chinese herbal cure called artemether, derived from the wormwood shrub. High-powered clinical trials are confirming its effectiveness in treating cerebral malaria and it's now being used in South-east Asia. At the moment, though, doctors in Africa are keeping artemether in reserve until actually needed.

Madagascar Nine out of 10 child victims of acute leukaemia survive. Many of them have a small Madagascan flower to thank. The rosy (or Madagascan) periwinkle (Catharanthus roseus) was investigated as a treatment for diabetes, but this proved unsuccessful. Then, in 1958, a compound called vinblastine was isolated from the plant, and proved an effective treatment for Hodgkin's disease. Another key drug, vincristine, was later identified - and is largely responsible for today's remission rate against some leukaemias.

Japan People suffering from allergies or blocked nasal passages are often prescribed a medicine containing ephedrine. The chemical is an alkaloid derived from Ephedra shrubs found in China and Japan. Ephedrine helps to clear blocked bronchial and nasal passages by reducing the swelling in the nose and throat, although its use in the treatment of conditions such as asthma has been largely superseded by safer drugs such as salbutamol.