Raphanus sativus var. niger

The black radish, a cultivated variety of the radish, is a root vegetable of the family Brassicaceae and is a variety of winter radish. It is also called black Spanish radish or Erfurter radish. The edible root has a tough black skin and white flesh. There are round and elongated varieties. Like other radishes, black radish has a sharp flavor due to various chemical compounds that the plant primarily uses as pest defense. Some of these phytochemicals are produced in high concentrations....read more on Wikipedia.