Geography and distribution
The Madagascar periwinkle is indigenous to Madagascar, but is cultivated and naturalised throughout the tropics and parts of the subtropics.
A tender, perennial plant which grows as a herb or a subshrub sprawling along the ground or standing erect (30 cm to 1 m in height). It has attractive white or pink flowers comprising five petals spreading from a long, tubular throat. The leathery, dark green leaves are arranged in opposite pairs. Each fruit is made up of two narrow, cylindrical follicles which house numerous grooved seeds. Like many other plants in the Apocynaceae family, the sap is a milky latex.
Threats and conservation
Madagascar’s forests have been heavily impacted by human activity, but the Madagascar periwinkle’s ability to thrive in disturbed areas has enabled it to survive in its island home. Furthermore, it is widely established in the wild throughout tropical regions of the world, commonly cultivated in gardens and homes, and grown commercially for the pharmaceutical industry. Given the modern ubiquity of naturalised and cultivated populations of Madagascar periwinkle, direct conservation measures are a low priority for this species.
A rainforest cure for cancer?
The Madagascar periwinkle was for many years grown simply as an attractive bedding plant in tropical areas. It comes in a range of pinks and reds that give rise to its other common name, the rosy periwinkle. But today it has a more serious purpose; planted around the world during colonial times, it quickly became known at the same time as a useful folk medicine for diabetics. American and Canadian researchers during World War Two became aware that soldiers stationed in the Philippines were using it instead of insulin during shortages.
As a consequence, after the war, lab testing was done in earnest on the Madagascar periwinkle. This revealed that the plant contained thirty alkaloids, strong plant chemicals that might be of use to humans. The leaves were found to contain two particularly valuable alkaloids, vinblastine and vincristine. These alkaloids work by disrupting part of cell division or ‘mitosis’, stopping the process when newly copied DNA is split into two identical parts to produce two identical new cells.
The drug company Eli Lilly tested the new chemicals on mice and found they helped to combat cancers, in particular those of the bone marrow such as childhood leukaemia and non-Hodgkin’s Lymphoma. They developed an effective chemotherapy treatment, and today the prognosis for sufferers has changed from a one in ten chance of survival, to at least an eight out of ten chance of some remission.
Contracts and collecting
Catharanthus roseus in situ
The Madagscar periwinkle shows how important it is to preserve areas of rich biodiversity, for there may be other 'miracle drugs' contained in plants just waiting to be discovered. But it also epitomises the issues involved in exploiting the riches of the plant world. In the 1960s, when these alkaloids were discovered, rich Western countries saw little need to reward the original homeland of the periwinkle, Madagascar, for the riches that had been earned from the plant.
Today at Kew we take a different view. We believe that Madagascar’s people should have a say over how their plant resources are exploited: particularly where a plant is restricted to a single country. The Convention on Biological Diversity, of which the UK is a signatory, states that rights to exploit a discovery like that of the alkaloids in the periwinkle should be shared fairly.
In practice, this means that Kew has a seven-person strong legal team whose job is it to make sure that things are done equitably. Before a plant collecting team can even book flights, contracts are drawn up to ensure that the country being visited is happy with the arrangements being made. With such contracts in place, local people have much more incentive to look after their biodiversity. Now they know that if a profitable discovery is made, they will have a share in it
Millennium Seed Bank: Seed storage
Kew's Millennium Seed Bank Partnership aims to save plant life worldwide, focusing on plants under threat and those of most use in the future. Seeds are dried, packaged and stored at a sub-zero temperature in our seed bank vault.
Number of seed collections stored in the Millennium Seed Bank: None
Seed storage behaviour: Orthodox (the seeds of this plant survive being dried without significantly reducing their viability, and are therefore amenable to long-term frozen storage such as at the MSB)
Composition values: Oil content: 34.4%; Protein: 19.4%
The Madagascar periwinkle is very easy to cultivate, and can be propagated by seed or by cuttings, but is sensitive to over-watering. A tender plant, it does not withstand frosts and is best grown indoors in temperate climates. It thrives well in hot and humid environments, in full sun or partial shade and flowers all year round in hot climates.
Catharanthus roseus is easily propagated by apical semi-ripen cuttings in light, free-draining compost. Best results are when bottom heat and high humidity are provided. Propagation by seed at 22-25ºC, kept in the dark until germination.