Life habit: lichenized Thallus: thin or thick, radiate-plicate marginal lobes, becoming rimose and finally areolate towards the center surface: whitish to light gray and heavily pruinose (morphotype I) or gray-brown to pale yellowish brown and mainly epruinose but occasionally pruinose around periphery (morphotype II) Apothecia: frequent, cryptolecanorine to lecanorine, adnate but frequently innate, 0.1-0.7 mm in diam. disc: black, often with a white pruina, plane or becoming convex; epihymenium: brown hymenium: hyaline, I+ blue; paraphyses: simple or weakly branched; hypothecium: brown or dark brown asci: cylindrical, 8-spored ascospores: brown, 1-septate, 8-12 x 5-8 µm, distinctly ornamented Pycnidia: immersed, obpyriform conidia: hyaline, simple, bacilliform, 7-11 x 1 µm Spot tests: K-, C-, KC-, P- or P+ orange (medulla) Secondary metabolites: 3-chlorodivaricatic acid (major), divaricatic acid (traces), occasionally norstictic acid (minor), occasionally 3-chlorolecanoric, 3-chloronordivaricatic and 3-chloroisosubdivaricatic acids (all minor) (chemotype I); divaricatic acid (major), 3-chlorodivaricatic acid (traces) (chemotype II); 5-chlorodivaricatic acid (major), 3-chlorodivaricatic acid (minor) (chemotype III); psoromic acid, 2'-O-demethylpsoromic acid (chemotype IV); virsenic acid (chemotype V). Substrate and ecology: on open siliceous rock outcrops, including lava flows at very dry and/or sunny sites at coastal sites to inland ones at moderate elevation World distribution: western Mediterranean Europe, northern Africa, Macaronesia, and southwestern North America Sonoran distribution: Californian Islands, the coastal mesas and canyons of the coastal mountains extending southwards into Baja California, including Guadalupe Island, and the Sonora side of the gulf of California, from sea level to 750 m. Notes: Dimelaena radiata is characterized primarily by the brown hypothecium, ascospores with a distinct ornamentation and its chemistry with a great infraspecific variation. A remarkable º of variation is also observed in the color and thickness of the thallus. Dimelaena radiata is separated from Buellia fimbriata (Tuck.) Sheard (recently synonymized with Buellia tesserata Körb.), a species that is similar in thallus color, chemistry (3-chlorodivaricatic acid) and ascospore ornamentation, by its radiate-plicate thallus margin and the lack of a fimbriate prothallus.