Branching out, it forms an encrusting, irregular patch, which is smooth and blue-grey or green-grey to yellowish-green on the upper surface. The tips tend to curl up revealing brown to black undersides. The thallus lobes are tube-like, semi-erect structures which grow from the outer edges and are covered in sordia (reproductive structures). Thallus 6 to 8cm broad.
It grows in a wide range of habitats, and found on twigs and branches, but also on rocks and walls. It can be an indicator of older forest growth. Common and widespread throughout the British Isles.