Also dai gai choy and variations (Chinese), Swatow mustard or cabbage, heading mustard
This is the mustard that appears most often in Asian and Oriental markets—fortunately, for it is a versatile and luscious green, as I hope you’ll agree the four recipes illustrate. Various forms of the ribbed, vaguely romaine-like leaves swirl into long flattened heads. Usually, their ruffly tops have been chopped and one sees only a thick cluster of tightly furled pale leaf-bases edged with darker green (central and right heads in photo). Raw, the mustard is ferocious and is traditionally tamed by salt-pickling (as for kimchee). Cooked, its fleshy stalks and leaves turn bright jade, bittersweet, and juicy.