This article is about the plant. For other uses, see Mustard. Brassica juncea, mustard greens, Indian mustard, Chinese mustard, Jie Cai (in Mandarin) or Kai Choi (in Cantonese), or leaf mustard is a species of mustard plant. Subvarieties include southern giant curled mustard, which resembles a headless cabbage such as kale, but with a distinct horseradish-mustard flavor.