The fruitbodies are erumpent, emerging from under the bark of oak twigs.  The surface is covered in pimples, which are the ostioles or projecting mouths of the spore-producing perithecia inside the fruitbody.  

Very similar barkspots occur on other species of deciduous tree

host

Good field photos, and you must identify species of host tree

On dead oak branches.

All year round.