Nasturtium

Every part of the naturtium is edible, although I've only had the flowers. (In a salad, if you're curious.)

The nasturtium originated in the Andes, where its tuberous root was used for food. It become a popular garden plant in Europe about 300 years ago. In fact, the variety in the foreground (with the darker leaves) was one of the most popular garden flowers in Queen Victoria's time. I can't remember the actual name though--maybe Empress of India? I really should keep better track of my plant labels...