The richest source of nutrients of all the land plants (also see seaweed), the greener they are the more nutritious they are.
There are many! Including chicory, collard greens, arugula, watercress, dandelion greens, kale, beetroot and mustard greens, rape, rocket, spinach, swiss chard, iceberg lettuce.
Protein, carbohydrate. Rich in chlorophyll, folic acid and vitamin A (the darker the leaf the higher the vitamin A content) and B-complex, C, E and K, calcium, magnesium, iron, potassium, phosphorus, soluble fibre, cellulose, inulin, sodium.
Some green leafy veggies, eg. spinach, beet greens and swiss chard, contain oxalic acid when raw. This interferes with the body's uptake of calcium and iron. Oxalic acid is destroyed by heat, so these vegetables should be cooked, even just lightly steamed.
Protect against cancer, antioxidant, helps protect the eyes (particularly against sun damage). Green leafy vegetables may help osteoporosis, to strengthen bones. Preventative against anaemia, especially for vegetarians. Useful for gout as they help reduce uric acid. Mouth ulcers, swollen gums, halitosis, relieve hot flushes.
Raw in salad. Or steam lightly (as they lose some of their nutrients when cooked). Or add to a number of dishes including soups, stir-frys, pies, stews, curries…