The Green Man

The Green Man, also known as “Jack in the Green” is an art motif, typically depicted as the head of a bearded man surrounded by or emerging from vegetation.

In some cases, the Green Man has leaves growing out of his head or mouth.
It’s quite a common motif in medieval European church architecture and has been widely reused as a decorative element in many other settings — once you know it, you start to see it everywhere.