Wikipedia:
Kale or borecole is a form of cabbage (Brassica oleracea Acephala Group), green or purple, in which the central leaves do not form a head. It is considered to be closer to wild cabbage than most domesticated forms.
The species Brassica oleracea contains a wide array of vegetables including broccoli, cauliflower, collard greens, and brussels sprouts. The cultivar group Acephala also includes spring greens and collard greens, which are extremely similar genetically.
Move over Popeye and make room for the "queen of greens," Kale. Gaining in popularity, Kale is an amazing vegetable being recognized for its exceptional nutrient richness, health benefits, and delicious flavor.
Eating a variety of natural, unprocessed vegetables can do wonders for your health, but choosing super-nutritious kale on a regular basis may provide significant health benefits, including cancer protection and lowered cholesterol.
Kale, also known as borecole, is one of the healthiest vegetables on the planet. A leafy green, Kale is available in curly, ornamental, or dinosaur varieties. It belongs to the Brassica family that includes cruciferous vegetables such as cabbage, collards, broccoli, and Brussels sprouts.
What makes Kale so exceptional? Here is why it's a superstar vegetable -- and ways to work it into your diet.

• Kale is a Nutritional Powerhouse

   

  One cup of Kale contains 36 calories, 5 grams of fiber, and 15% of the daily requirement of calcium and vitamin B6 (pyridoxine), 40% of magnesium, 180% of vitamin A, 200% of vitamin C, and 1,020% of vitamin K. It is also a good source of minerals copper, potassium, iron, manganese, and phosphorus.

  Kale’s health benefits are primarily linked to the high concentration and excellent source of antioxidant vitamins A, C, and K -- and sulphur-containing phytonutrients.

  Carotenoids and flavonoids are the specific types of antioxidants associated with many of the anti-cancer health benefits. Kale is also rich in the eye-health promoting lutein and zeaxanthin compounds.

  Beyond antioxidants, the fiber content of cruciferous Kale binds bile acids and helps lower blood cholesterol levels and reduce the risk of heart disease, especially when Kale is cooked instead of raw.

   

• Super-Rich in Vitamin K

  Eating a diet rich in the powerful antioxidant vitamin K can reduce the overall risk of developing or dying from cancer, according to a study in the American Journal of Clinical Nutrition. Vitamin K is abundant in Kale but also found in parsley, spinach, collard greens, and animal products such as cheese.
  Vitamin K is necessary for a wide variety of bodily functions, including normal blood clotting, antioxidant activity, and bone health.
  Note well: Too much vitamin K can pose problems for some people. Anyone taking anticoagulants such as warfarin should avoid Kale because the high level of vitamin K may interfere with the drugs. Consult your doctor before adding Kale to your diet.
  Kale might be a powerhouse of nutrients but is also contains oxalates, naturally occurring substances that can interfere with the absorption of calcium. Avoid eating calcium-rich foods like dairy at the same time as kale to prevent any problems.

• Eat More Kale

  In summer, vegetable choices abound. But during the cooler months, there are fewer in-season choices -- with the exception of Kale and other dark, leafy greens that thrive in cooler weather.
  To find the freshest Kale, look for firm, deeply colored leaves with hardy stems. Smaller leaves will be more tender and milder in flavor. Leaves range from dark green to purple to deep red in color.
  It is recommended that you store Kale, unwashed, in an air-tight zipped plastic bag for up to five days in the refrigerator.

• Easy Ways to Prepare Kale

  Quick cooking preserves Kale's nutrients, texture, color, and flavor. Rinse Kale, chop it finely, and add it soups, stews, stir-frys, salads, egg dishes, or casseroles. Or top pizzas with Kale for added nutritional goodness. Steam Kale for five minutes to make it more tender or eat it raw. You can also substitute it for spinach or collard greens in recipes.

• Other fast and easy ways to prepare Kale:

  
  -Make a simple salad with a bunch of thinly sliced Kale, red pepper, onion, raisins, and your favorite salad dressing.
  -Braise chopped Kale and apples, garnish with chopped walnuts, and add a splash of balsamic vinegar.
  -Toss whole-grain pasta with chopped Kale, pine nuts, feta cheese, and a little olive oil.
  -Cover and cook a pound of chopped Kale with a few garlic cloves and 2 tablespoons olive oil for 5 minutes; season with salt, pepper, and a tablespoon of red wine vinegar.
  -Make Kale chips by slicing Kale into bite-size pieces, toss with a drizzle of olive oil and a pinch of salt, and bake for 10-15 minutes at 350 degrees in the oven.

  All vegetables are rich in nutrients and fiber, fat-free, and low in calories and are intended to be the cornerstone of all healthy diets. Toss Kale into your grocery cart to enrich the nutritional goodness of your diet and help you eat the recommended 4-5 servings of vegetables every day.