Solanum is a large and diverse genus of flowering plants, which include three food crops of high economic importance, the potato, the tomato and the eggplant. It also contains numerous plants cultivated for their ornamental flowers and fruit.
The species most commonly called nightshade in North America and Britain is Solanum dulcamara, also called bittersweet or woody nightshade. Its foliage and egg-shaped red berries are poisonous, the active principle being solanine, which can cause convulsions and death if taken in large doses. Solanum dulcamara has been valued by herbalists since ancient Greek times. In the Middle Ages the plant was thought to be effective against witchcraft, and was sometimes hung around the neck of cattle to protect them from the "evil eye".