Wall rue (Asplenium ruta-muraria)

''Asplenium ruta-muraria'' is a species of fern commonly known as wall-rue . In Germany, it is known as Mauerraute or Mauerstreifenfarn. It is a very small epipetric species, growing exclusively on limestone and other calcareous rocks. Its fronds are bluish-green and are heavily sub-divided, becoming up to 12cm in length.