"Greens" is a generic term referring to hearty cooking greens such as kale, collards, turnip greens, and mustard greens. Slightly bitter in varying degrees, all greens are packed full of healthy protein and vitamins. Kale has an assertive peppery flavor and frilly edges; it adds a nice punch when added raw to salads. Collards are a form of kale, with thick, dense leaves and a flavor that's slightly milder and more cabbagelike than kale's. A Southern favorite, collards are best when cooked until tender, perhaps with the addition of a salty pork product. Turnip greens are medium-size leaves with a slightly ruffled edge and a pungent biting flavor that mellows with cooking. Similarly pungent, mustard greens are small leaves with a distinct aroma of mustard. Greens prefer a cooler growing climate, though they are available year-round in most of the country.