Kale or Collard is loosely related to cabbage, or at least from a culinary angle. Kale has a coarse texture and a mildly bitter taste. Kale was a staple in Scotland, e.g. for kail brose, a soup. Collard greens are a traditional dish with pork from the southern states of the USA.
Dowell, P., Bailey, A. (1980) The Book of Ingredients, Dorling Kindersley. ISBN 0718119150.