Lettuce live right! Romaine lettuce is a terrific source of beta-carotene, while arugula is a great source of calcium. Endive provides fiber and folate while mustard greens add tyrosine. Get vitamins A and C from bok choy, and the antioxidants lutein and zeaxthanin from spinach. Mix up these potent greens for a garden-variety style salad! The more the merrier!