This frilly member of cabbage family can be dark green or red. It is in season most of the year, and can grow in harsh frosty climates where other greens don't do so well. Kale was an important food in Europe until the end of Middle Ages when the cabbages we know today were bred. In Scotland, where it is traditionally a key part of the diet, it is called kail.
IN THE KITCHEN
Chop it and use in place of spinach or cabbage in cooked dishes (it's best not to serve it raw). Kale works especially well with wintry food such as soups, stews, beans, root vegetables, potatoes, ham, and game. It can be steamed, stir-fried or boiled. Try mixing it into bubble and squeak, fish pie, or curries. Scots brose, a nourishing soup or oatmeal, is one of the best traditional dishes.
There are many different varieties of kale available to gardeners, including some with silver and purple variegated leaves, however curly kale, which has crimped, frilly leaves is most widely available in stores and markets. Plain-leaved kale tastes so strong that it tends to be used as animal feed. Sea kale is a different plant.