Utilized as seeds as well as oil, mustard is a versatile vegetable that is less popular than its fellow green friends. The leaves hold a texture similar to that of collard greens and kale, yet they present a truly unique tang of peppery sensation. The vegetable is widely popular in Indian, Japanese, and Chinese cuisine. While they are rather bitter as well, the leaves can be countered with a small amount of salt per taste. Mustard greens are rich in Vitamin A, Vitamin C, Vitamin K, folate, and manganese. Take note that the FDA has marked mustard oil as toxic for human consumption.