Son of a beech.
Two tall trees, a Beech and a Birch, are growing in the woods. A small tree begins to grow between them, and the Beech says to the Birch, "Is that a son of a Beech or a son of a Birch?" The Birch says he cannot tell, but just then a woodpecker lands on the sapling.
The Birch says, "Woodpecker, you are a tree expert. Can you tell if that is a son of a Beech or a son of a Birch?"
The woodpecker takes a taste of the small tree and replies, "It is neither a son of a Beech, nor a son of a Birch. It is, however, the best piece of Ash I have ever poked my pecker into."