Note: Do not rely on this information. It is very old.
Periwinkle
Periwinkle, the popular name of the gentis Vinca, two species of which, doubtfully indigenous, are the only British representatives of the considerable tropical drder of Gamopetala; (q.v.), Apocynacese. They are prostrate perennial evergreen herbs, with wiry stems; opposite, ovate, leathery leaves; and salver-shaped, blue, white, or redflowers, an inch or more across. There are five petals: the corolla-tube is hairy inside, and has five included epipetalous stamens; and there are two superior many-seeded carpels and a single style. There is a poisonous milky latex.