I should point out that the green on the mask is darker and more 'plant' green than the picture. The photographer has been given a stern talking too...
Historical note:
A Green Man is a sculpture, drawing, or other representation of a face surrounded by or made from leaves. Branches or vines may sprout from the nose, mouth, nostrils or other parts of the face and these shoots may bear flowers or fruit.
Superficially the Green Man would appear to be pagan, perhaps a fertility figure or a nature spirit, similar to the woodwose (the wild man of the woods), and yet he frequently appears, carved in wood or stone, inchurches, chapels, abbeys and cathedrals, where examples can be found dating from the 11th century through to the 20th century.