These leafy greens are members of the cabbage family, and so are classified as a cruciferous veg. They can be used where other leafy greens can, including soups, sauces, and salads.
Being a relative of the cabbage, they pack a little (big) green punch of vitamins and phytonutrients, including dietary nitrates. Cruiferous veg have extremely powerful health benefits including reduced risk of cardiovasular disease.