Endohyalina

Endohyalina is a genus of 10 species of corticolous (bark-dwelling) crustose lichens in the family Caliciaceae. These lichens either form thin, tightly attached crusts on tree bark or live as parasites on other lichens, sometimes becoming so reduced that they are nearly invisible to the naked eye. They produce small, black, disc-shaped fruiting bodies that begin buried in the crust and later emerge flush with the surface, containing spores that are divided once by a cross-wall and darken to brown as they mature. ...read more on Wikipedia.