Thallus: crustose, typically continuous, even to tuberculate, but rarely coarsely tuberculate or tuberculate-plicate, sometimes scurfy, usually distinctly rimose in thick specimens, thin to thick, forming extensive patches up to several dm in diam.; prothallus: often conspicuous, white, felty, composed of radiating hyphae forming a marginal border to about 1 cm wide surface: gray and/or white, sometimes with a brownish tinge (in herbarium specimens only?), sorediate soredia: forming coarse consoredia, up to 90-125 µm in diam., often mixed with eroding cortex fragments, in pale yellow to greenish white (rarely pure white and sometimes becoming pink in the herbarium) irregular soralia often somewhat elongate and angular and usually delimited by a ±raised rim formed by the cortex and often to a cm or more wide or sometimes becoming confluent and accounting for most of the thallus cortex: light to dark gray, sometimes bluish gray, rarely white medulla: not evident to distinct and white; photobiont: green, up to 18 µm in diam. Apothecia: rare, immersed in thalline verrucae or +flush with the thallus surface, 0.2-0.4 mm wide disc: gray-black, white pruinose margin: ±elevated hymenium: up to 240 µm tall asci: broadly clavate to cylindrical-ellipsoid, with thickened, I- apex, up to 210 x 55 µm, 1-spored ascospores: hyaline, muriform, ellipsoid, not apiculate, (75-)100-150(-205) x 25-50(-53) µm Pycnidia: rare (not known in Sonoran material): semi-globose to globose, black but covered in pruina conidia: bacilliform, 3-3.5 x 0.75-1 µm Spot tests: K+ yellow turning orange-red, C-, KC-, P+ yellow to orange Secondary metabolites: norstictic acid (major), connorstictic acid (usually a trace). Substrate and ecology: on bark (Quercus, Lithocarpus); rarely on rock elsewhere World distribution: Africa (the Canary Islands), Asia, Europe, and North America Sonoran distribution: southwestern California at 400-1990 Note: Apparently Phlyctis argena is closely related to P. speirea but is distinct by the presence of its soredia.