Dark green leafy vegetables are great sources of nutrition. Salad greens, kale and spinach are rich in vitamins A, C, E and K, and broccoli, bok choy and mustard are also rich in many of the B-vitamins.he vitamin K contents of dark green leafy vegetables provide a number of health benefits including: protecting bones from osteoporosis and helping to prevent against inflammatory diseases. Because of their high content of antioxidants, green leafy vegetables may be one of the best cancer-preventing foods.