Thallus crustose, leprose, diffuse, 100-500 µm thick, pale to mid blue-grey in herbarium, brighter and greener in the field. Granules fine, 60-120 µm diam., ecorticate, without projecting hyphae. Lower part of thallus of decolourized granules but true medulla absent. Photobiont a green alga, cells spherical, 8-15 µm diam., sometimes divided into autospores.
Chemistry: zeorin and usnic acid. Spot test reactions of acetone extract on filter paper: K-, C-, KC+ yellow, Pd-. The KC reaction can also be observed by swabbing the spot of K from the thallus onto tissue paper and adding C.