Hard cushion shaped stroma growing out of the bark of trees, usually birch.  Each has a bumpy, knobbly surface formed by the raised ostioles through which the spore are eventually ejected.  The ostioles are papillate - they have a small nipple-like projection in the centre.   The stroma are intially reddish-brown, becoming dark brown or black.  Often coalescing to form a larger mass. 

Other barkspots and woodwarts are associaed with different species of trees

host

Photograph in habitat; note substrate and associated tree species

Usualy on birch, sometimes Alder or rarely another species of tree

It appears all year round.