Life habit: lichenized Thallus: squamulose, monophyllous, sometimes disintegrating when old, up to 30(-40) mm wide, rounded or elongate, adnate, contiguous, rarely, slightly imbricate surface: olivaceous brown to brown, often with white edges, otherwise epruinose, concave, esorediate upper cortex: apparently formed by a growth zone in the algal layer pushing hyphae and algae up into the cortex ("Kegelrinden" of the Squamarina-type) but algal cells no longer visible, with thick-walled hyphae, anticlinally to irregularly arranged, 70-200 um thick, with an epinecral layer medulla: white, containing crystals of Ca-oxalate, I- photobiont: primary one a chlorococcoid green alga; secondary one absent; algal layer: discontinuous lower cortex: absent Ascomata: apothecial?, effuse, continuous with the thallus, laminal, several per squamule, discrete when young but soon becoming confluent and extending over the whole squamule surface disc: red-brown, only subtlty different by color from the cortex, becoming convex, epruinose exciple: lacking (thalline or proper) hymenium: developed within the upper cortex, initially formed by paraphyses and subsequently including ascogenous material; paraphyses: branched and anastomosing, thin-walled, apical cells not or slightly wider than base asci: clavate, surrounded by an amyloid, gelatinous sheath, containing a well developed, amyloid tholus with a deeper amyloid tube and usually an ocular chamber, 8-spored cospores: hyaline, simple, ellipsoid to subglobose, 13-17 x 7-9 um, without a halo Conidiomata: pycnidial, immersed in thallus, visible only as a faintly paler pore, with richly branched conidiophores producing conidia terminally conidia: hyaline, bacilliform to asymmetrically bifusiform, 8-10 x c. 1.5 um Spot tests: all negative Secondary metabolites: unidentified triterpenoids. Substrate and ecology: on gypsiferous soil World distribution: Euroasia, especially in arid and semi-arid habitats, from Austria to Mongolia and western North America, Greenland Sonoran distribution: two localities in NW Arizona. Notes: By developing ascocarps inside the thallus, the ascocarp ontogeny of Gypsoplaca resembles that of some parasymbiotic fungi. In this regard the ontogeny is rather similar to the thallinocarp development of Lichinella in the Lichinaceae, but the thallinocarp differs in that the asci are directly formed among thalline hyphae and living algae. In Gypsoplaca the hymenium is formed by paraphyses. Some secondary product variation is noted by Timdal (1990), but only one species is currently recognized.