Well, in Europe it was very common up until Middle Ages' end.  In fact, of the green vegetables, it was the most common!
Ha! Until the end of the Middle Ages, kale was one of the most common green vegetables!
Kale is so good for you. I try to eat it every day. Nice!  I know that kale leaves don't make a head, like headed cabbages do.  Also, their leaves can be purple or green! Oh cool.  Do you know anything about the history of kale?
Until the end of the Middle Ages, kale was one of the most common green vegetables in Europe.