Catharanthus roseus: Madagascar Periwinkle
If you were to encounter the plant, Catharanthus roseus (syn. Vinca rosea), in the wild for the first time you would hardly believe it was not a house plant. Even its name, derived from the Greek words katharos, meaning flawless, pure, and anthos, meaning flower, is extremely apt. The low, compact ‘shrublets’ with dense, glossy foliage and fairly large pink, 3.5 cm (VU in) across, reach a height of 30 to 70 cm (12 to 28 in), depending on the site and available nourishment.
Members of this species are to be found in all tropical countries, always in warm, sunny situations, often on sand flats or sand banks. The colour of the flowers, however, is not always pink, but varies from pure white, through white with a pink ‘eye’ in the centre, to dark crimson — colours which are found also in cultivation.
Though it is a perennial, catharanthus is often grown as an annual in Europe. If sown very early in spring it flowers from as early as midsummer continuously until the frost, so that it can be used, for instance, as a window-box plant. It overwinters well in a cool room and will produce flowers the following year in late spring.
Some years ago this plant became the focus of attention of medical science concerned with cancer research, for it was found to contain alkaloids (vegetable poisons) that have a significant effect on certain types of cancer. This, of course, is not meant as a recommendation but on the contrary as a warning to the reader, for the plant is extremely poisonous!
The best method of cultivation is to sow seeds in February, grow the plant until it flowers, then hard prune it in autumn, using the prunings as cuttings and trying to preserve the parent plant. The cuttings root rapidly and survive the winter better than older plants, often without damage even in a warm room. The substrate should be moderately heavy, relatively nourishing and porous, such as John Innes potting compost.