Thallus fruticose or palmate-foliose, heteromerous, of very variable morphology, branches terete to distinctly flattened, corticate, commonly dimorphic, fertile branches larger than shorter, and often ± richly branched, sterile branches. Cortex continuous and of equal thickness in terete species, or forming a markedly thicker upper layer and a thinner lower layer in flattened, dorsiventral species, of thick-walled, laterally fused, unorientated hyphae. Photobiont green, , confined to a distinct layer between cortex and medulla, cells single, spherical, (5-)6-12 µm diam. Medulla of longitudinally orientated, colourless, thick-walled hyphae. Apothecia terminal or subterminal, apical, subapical to ventral, often with sterile margins, producing a characteristic mazaedium composed of sterile elements and spores freed from asci which form a loose, dry, black or brownish-black powdery mass which may be partly covered by an enclosing receptacle. Asci 8-spored, clavate to cylindrical, wall disintegrating at an early stage of development liberating partially mature spores into hymenium. Ascospores simple, spherical to broadly ellipsoid, colourless, grey or brown or purplish-brown, often with a dense deposit of carbonaceous material on the outer surface.