An unlikely relative of the turnip family, this large leafy green is grown almost exclusively in Japan, Taiwan and Korea. Komatsuna gets its name from the Komatsugawa district, which includes Edogawa, Katsushika and Adachi wards. Tokyo was the second-largest regional producer of komatsuna in 2004. It is also called spinach mustard, Komatsuna has dark green leaves that are rich in calcium and often quite glossy. They can be harvested at any stage and prepared like spinach in the early stages and more like cabbage as they mature. The flavor grows stronger and hotter the longer the leaves mature. This versatile green can be stir-fried, pickled, boiled and added to soups or used fresh in salads.