Heterodermia  

Thallus small, foliose, in rosettes or irregular, sometimes combining to form extensive radiating mats. Marginal lobes discrete or contiguous and closely adpressed or ribbon-like, sometimes ascending and loosely attached, white to greyish, almost always fringed with cilia that are unbranched or abundantly branched. Upper cortex of periclinal hyphae. Lower surface pale or darkening or yellowish in part or completely, with or without a cortex, when present, of periclinal hyphae and with simple or branched, pale to black rhizines, marginal and sometimes long, extending beyond the thallus margin. Soredia, lobules or isidia usually present. Photobiont chlorococcoid.
Anamorph: conidiomata pycnidial, blackened, immersed. Conidia bacilliform to short-cylindrical.
Teleomorph: ascomata apothecia, very rare in most species; disc brown-black. Thalline exciple thick, incurved, subhymenium pale. Asci 8-spored, Lecanora-type. Ascospores very thick-walled, 1-septate, often with 1-3 additional small locules beyond the main locules, brown, cylindric-ellipsoidal, surface smooth, Pachysporaria-type.
Chemistry: atranorin (upper cortex), zeorin and other terpenes, β-orcinol depsides and depsidones and pigments occasionally also present (medulla).