Animal, vegetable or mineral?

What do you think this thing is?  It came in a bag of vegetables from a friend's garden.  It's very hard like a potato with a couple green leaves sprouting from the end.  I was stumped and had to ask.  A recipe came with the answer... slice thinly and fry until crisp and tender.  It's a kohlrabi.  And the kohlrabi chips were tasty!