Thallus: foliose to subfruticose, small to medium sized, moderately to very loosely attached, sometimes combining to form extensive, radiating mats, lobate lobes: linear to sublinear, elongate to shorter, discrete or contiguous; tips rounded or flabellate, sometimes ascending, with or without marginal cilia; cilia: black or pale upper surface: white, ivory white or gray to dark greenish brown, with or without pruina, with or without soredia or isidia upper cortex: prosoplectenchymatous, composed of periclinal hyphae medulla: white or sometimes yellow pigmented photobiont: primary one a trebouxioid alga, secondary photobiont absent lower cortex: lacking or prosoplectenchymatous, but sometimes only weakly organized and poorly differentiated from the medulla lower surface: surface pale or darkening; sparsely to rather densely rhizinate; rhizines: pale or darkening, simple or branched, sometimes protruding beyond the margin as seen from above Apothecia: present or absent, with a thalline exciple; subhymenium: hyaline asci: cylindrical, subclavate to clavate, Lecanora-type, 8-spored ascospores: , smooth, brown, thick walled, 1-septate, 15-54 x 7-25 µm Pycnidia: blackened and immersed conidia: bacilliform to short-cylindrical, 4-6 x ± 1 µm Secondary metabolites: terpenoids; ß-orcinol depsides and ß-orcinol depsidones and various pigments Geography: primarily pantropical with a few species extending into temperate areas, North America, Europe, Australasia, Asia and Africa Substrate: bark or wood, rock or rarely soil. Notes: Kurokawa (1962) published a definitive world monograph of the genus Anaptychia in which 72 predominately tropical species were treated. Subsequently, that genus was recognized as heterogeneous by Poelt (1965), who separated the genus Heterodermia with smooth, thick-walled spores and the constant occurrence of atranorin in the upper cortex from Anaptychia, all species of which have Physconia-type spores and lack atranorin in the upper cortex. All but nine of Kurokawas originally recognized species have been transferred to Heterodermia. This delimitation is now widely accepted, and also by Kurokawa (1998).