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DescriptionThallus: foliose, up to 7 cm in diam., usually ± regular and orbicular; lobes: rather linear and discrete to more irregular-flabellate and contiguous, 1-2 mm broad, ± flat and prostrate; upper surface: gray to gray-brown, completely to rather incompletely (lobe ends only) pruinose; without soredia or isidia, but becoming sparsely to rather abundantly lobulate; lobules: marginal, up to 0.5 mm across; upper cortex: paraplectenchymatous; medulla: white; lower cortex: irregularly prosoplectenchymatous, indistinctly delimited from the medulla in part; lower surface: mostly pale, white to very pale tan at the periphery and on most of the lower surface, scattered areas in older parts becoming tawny to very pale brownish, dull; rhizines: pale or darkening in older parts, often largely simple to furcate but with at least some becoming squarrosely branched; Apothecia: sometimes frequent but commonly missing from even large thalli, up to 2.5 mm in diam., the margin entire or becoming lobulate; ascospores: 28-33 x 14-16 µm; Spot tests: all negative; Secondary metabolites: none detected.; Substrate and ecology: on bark; World distribution: western North America, especially California; Sonoran distribution: southern California and Isla Cedros (Baja California).; Notes: This species is similar to some forms of the normally fertile species, Physconia americana, from which it is distinguished primarily by the pale lower surface and the more regularly lobulate upper surface. With poorly developed specimens, it can be difficult to distinguish between these two species. When well developed, P. californica bears a marked superficial resemblance to two lobulate species known from Japan, P. lobulifera Kashiw. and P. hokkaidensis Kashiw. Both these taxa have a black lower surface and a scleroplectenchymatous upper cortex.