Catharanthus roseus (L.)G.Don Apocynaceae. Madagascar Periwinkle Distribution: Madagascar. It is the source of vincristine and vinblastine, which impair cell multiplication by interfering with microtubule assembly, causing metaphase arrest and are effective medications for leukaemias, lymphomas and some solid tumours. The mortality from childhood leukaemia fell from 100% to 30% once it was introduced - not a drug that could ethically be tested by double-blind trials. These chemicals were initially discovered by investigators in 1958 who were looking for cures for diabetes so tested this plant which was being used in the West Indies to reduce blood sugar levels. There are 70 different alkaloids present in this plant, and some - catharanthine, leurosine sulphate, lochnerine, tetrahydroalstonine, vindoline and vindolinine - lower blood sugar levels. However, the toxicity of this plant is such that this is not a plant to try at home for diabetic management. The vincristine content of the plant is 0.0003%, so two kilograms of leaf are required to produce sufficient vincristine for a single course of treatment for a child (6gm). Fortunately it is a vigorous weed and easy to grow in the tropics. Artificial synthesis has now been achieved. Photographed in the Medicinal Garden of the Royal College of Physicians, London.