Son of a gun! We thought we were pretty well versed in odd veggies, but we had never heard of this one until recently. These black radishes, known as mooli in India, are from Spain. They are roughly the size of turnips, so tend to be a little larger and tougher than the red variety you are probably used to seeing.
You should consult your doctor before eating the Spanish black radish as they can have a profound effect on your liver and/or gallbladder. (Please note that many holistic treatments use the black radish to treat ailments of the liver and gallbladder.) There is also current study to see if this vegetable may have anti-cancer properties due to its possible detoxification effect on the Hep G2 human hepatoma cells.