Periwinkle

Ever since people in tropical regions around the world began to grow Madagascar periwinkle (Catharanthus roseus) for its cheerful pink flowers, the plant has been known as a home remedy for diabetes. In the 1950s, when researchers began testing periwinkle for its anti-diabetic properties, they discovered several highly toxic alkaloids in the plant's tissues. Two of them led to key drugs for cancers of the blood: vinblastine and vincristine.

(Podcast: The Plant Detective, 8/9/14)