Thallus: variable, usually crustose, rarely squamulose, compact, forming effigurate, or rarely placodioid, delimited rosettes up to 2 cm in diam., with marginal lobes up to 2(-3) mm wide and 0.3 mm thick with rounded apices and usually with a distinctly raised margin up to 0.5 mm thick, usually becoming contiguous with other thalli forming a coarse, irregularly spreading, +continuous crust up to a dm or more wide upper surface: whitish gray to pale yellowish gray, even to rough, supporting numerous horizontal to vertical, regular to irregular and deformed, fragile, +dorsiventral, sometimes capitate, easily detached lobules acting as diaspores lobules: apparently evolve partly by budding off from lobe margins and partly from the upper surface, and perhaps also from disintegrating lobes soredia: few or absent medulla: distinct in thick specimens, white; photobiont: aggregated in globose groups 24-50 µm in diam. in the diaspores and as a +continuous layer just beneath the surface of the thallus lower surface: whitish gray, without a tomentum Spot tests: K-, C-, KC-, P+ or Secondary metabolites: chemotype I (most specimens): atranorin (minor), pannaric acid 6-methyl ester (major), usually roccellic or rangiformic acids (major) and possibly methyl porphyrilate, pannaric and phorphyrilic acids (all as trace); chemotype II: norascomatic acid (major), strepsilin (minor), isostrepsilic acid (minor), atranorin (minor) and chloroatranorin (minor). Substrate and ecology: on dry soil, rarely on bare rock and wood in grasslands, coastal scrub, chaparral to desert transition areas, mixed oak-chaparral-pasture and oak forests World distribution: Europe (chemotype I only), North America (along the Pacific coast from Mexico as far north as Marin Co., California Sonoran distribution: southern California, and Baja California, from sea-level to 1250 m. Notes: Lepraria xerophila is a polymorphic but distinctive species varying from squamulose and then superficially resembling a cushion of Cladonia squamules, to crustose with an effigurate to placodioid margin. The squamulose forms are rare. The well-defined photobiont layer (two in some specimens) in the thallus adds to the distinctiveness of this species. The form and size of the consoredia are also variable, probably at least partly due to the fact that they may originate from both the upper surface and from the lobe margins. In some specimens the thallus surface supports numerous small thalli or lobes, but it was not evident if they originated in situ or if they settled there as diaspores or consoredia after having been produced elsewhere. Diaspores of similar size and form, as in L. xerophila, are also seen in some specimens of L. vouauxii. Lepraria vouauxii is chemically similar to L. xerophila in producing the dibenzufuran pannaric acid-6-methyl ester, but is distinct in containing 4-oxypannaric acid-6-methyl ester as a diagnostic substance, and in only rarely producing atranorin (and then only in trace amounts; from a contaminant?); roccellic acid is an accessory in trace amounts only, and rangiformic acid is not known from that species. In North America, Lepraria xerophila has been found in strictly coastal sites from Baja California Sur in the south (24degreeN) as far north as Marin Co. in northern California (37degreeN). Its center of distribution appears to be the islands of southern California. According to label data (Weber, Lich. Exs. 455, distributed under the name "Siphula (?) sp.") it is "undoubtedly the most abundant earth lichen in coastal southern California". Chemotype I is widespread and common; chemotype II is rare is represented by only a few specimens from southern California in the Channel Islands.