Life habit: +parasitic on algal colonies, lichenicolous or saprobic Thallus: usually indistinct Ascomata: apothecia short- to long-stalked, black or stalk pale below stalk: +colorless in central part, usually brown, reddish or greenish in outer part; hyphae: periclinally to irregularly arranged capitulum: obovoid to lenticular; mazaedium: not developed true exciple: ±well developed, composed of a few rows of periclinally arranged or interwoven hyphae hymenium: covered by a thin, dark epithecium; paraphyses: absent asci: formed singly from asccogenous hyphae with croziers, cylindrical to subclavate, 25-55 µm long, with strongly thickened apex often penetrated by a narrow or short and wide canal; persisting until ascospores mature, 8-spored ascospores: not aggregated into a dry spore mass, simple or 1-septate, ellipsoid to oblong- or fusiform-ellipsoid, pale to dark brown or with an aeruginose tinge, (3.5-)5-10(-14) x (1.5-)2-4(-5.5) µm; septum colorless to dark brown; wall: medium thick, dark brown; surface smooth to minutely warted but without irregular cracks Conidiomata: some species with coelomycetous anamorphs, either pycnidia, with walls of outwardly pointed cells (Asterophoma), amongst the spore-masses of host Caliciales, or sometimes borne on long, branched stalks; conidiogenous cells: narrowly ampulliform to sub-cylindrical, arising singly, enteroblastic, acrogenous; other species with hyphomycetous anamorphs, both of a simple, Phialophora-like type and a rather complex, catenulate anamorph with rather large conidia belonging to Catenomycopsis conidia: rod-shaped to oblong-ellipsoid, simple, colorless, 2-3.5 x 1 µm Secondary metabolites: ascomata with various pigments Substrate: mostly on dry bark or wood of old, hollowed or dead trees, also on Cladonia squamules, rotting wood polypores and under rock overhangs Geography: cosmopolitan; many species occurring in cool temperate to temperate areas, while other species are restricted to the tropics. Notes: Chaenothecopsis is characterized by a stalked capitulum lacking a mazaedium, short asci (less than 55 µm long) with a central canal in the thickened tip and simple or 1-septate spores. It is distinguished from Calicium, Chaenotheca and Microcalicium by the ascospores not forming a dry spore-mass (mazaedium). Mycocalicium, Phaeocalicium and Stenocybe differ in having a uniformly thickened ascus apex, and the last two genera have larger ascospores. Identification of species in this genus is often difficult. It is essential to study anatomical details on high-quality, c. 10 µm thick microtome sections. Chemical reactions must be studied under the microscope and some of the K+ reactions fade rapidly and might easily be overlooked. The study of details such as ascus apices or exciple and stalk structure is often facilitated if the sections are stained by Lactophenol Cotton Blue and heated gently, or by some faster dye such as Congo Red in moderate concentration. Generic delimitiations in Mycocaliciaceae are in need of revision.