Mizuna (Brassica rapa var. nipposinica) is a Japanese mustard green known for its deeply serrated, feathery, glossy dark-green leaves carried on slender, crisp white stalks. It eats with a clean, fresh, peppery-mustard bite that is far gentler than arugula or the hotter Asian mustards — bright and lively rather than fiery — which is why it has become a staple of mixed salad-leaf blends as well as a quick-wilting green for Japanese hotpots, soups and pickles.