The rosy periwinkle (Catharanthus roseus) is native only to the tropical forests of Madagascar, the world's fourth largest island, found off the east coast of Africa.

This pretty plant gives us two very important cancer-fighting medicines: vinblastine and vincristine.

Vinblastine has helped increase the chance of surviving childhood leukaemia from 10% to 95%, while vincristine is used to treat Hodgkins' Disease.

Traditional Madagascan healers used the rosy periwinkle for treating diabetes. This led to its study by western scientists who then discovered its anti-cancer properties.

These medicines have proved very profitable for global drug companies. Worldwide sales are worth over £75 million a year, but virtually none of this money finds its way back to Madagascar, one of the poorest countries in the world. Recent international agreements have tried to ensure that more profits from the commercial development of animal and plant species return to the countries of origin.