Life habit: lichenized, or occasionally lichenicolous Thallus: verruculose-granular or immersed (usually not on other lichens) surface: gray to gray-green, pale yellow-green or dark green photobiont: primary one a Trebouxia green alga, secondary one absent Apothecia: usually with long or short stalk, rarely sessile, black or with a brown tinge stalk: sclerotized, blackish brown to greenish black, irregularly interwoven hyphae capitulum: globose to lens-shaped, often with pruina on various parts true exciple: well developed, supporting the dry spore mass asci: cylindrical to clavate, formed singly from ascogenous hyphae with croziers, dissolving at an early age ascospores: 1-septate, ellipsoid or broadly ellipsoid, 6-16 x 3-8 µm, forming a well developed, black, dry spore mass (mazaedium); wall: thick, dark brown, often with a distinctive ornamentation, without gelatinous coat Conidiomata: pycnidial, sessile or slightly immersed, simple, globose; ostiole: punctiform; conidiophores branched; conidogenous cells: subcylindrical, enteroblastic conidia: broadly ellipsoid to short-cylindrical, colorless, non-septate Secondary metabolites: ß-orcinol depsidones and para-depsides, xanthones, anthraquinones, usnic acids, and pulvinic acid derivatives Substrate: usually on bark or wood, or occasionally on siliceous rocks, in rather humid and sheltered situations Geography: cosmopolitan, mostly in cool to temperate areas. Notes: Calicium resembles Cyphelium in thallus morphology, apothecial anatomy, chemistry and ecology but differs in the apothecia being stalked or rarely almost sessile but never immersed.