Thallus: foliose, 2-6(-10) cm in diam., loosely adnate, irregularly lobate lobes: irregular, short to elongate, finely lobulate to lacerate, +plane, separate, 0.5-3 mm wide, 70-170(-200) µm thick; apices: rotund, entire to granular, often wavy, usually erect upper surface: brown to olivaceous or greenish brown, initially smooth, usually wrinkled, sometimes with granular to isidiform lobules, particularly towards the margins, not isidiate internal anatomy: with upper and lower cortices consisting of a single layer of irregularly isodiametrical cells 6-13 µm in diam., internally with loosely interwoven chains of Nostoc and hyphae lower surface: light gray to cream-colored, smooth, with scattered tufts of white hairs Apothecia: common, laminal, sessile, 0.1-1 mm wide disc: brown to dark red-brown, concave to plane to convex margin: thalline, concolorous with the thallus, smooth or granular or lobulate exciple: euparaplectenchymatous, 20-60 µm thick centrally hymenium: hyaline below and thinly yellow to brown above, 150-200 µm tall; paraphyses: unbranched, 1-2 µm wide, slightly inflated apically; subhymenium: pale yellow, 35-70 µm thick asci: cylindrico-clavate, 8-spored ascospores: hyaline, muriform, 3-7-septate transversely, 1-2-septate longitudinally, ellipsoid to subfusiform, 25-45 x 12-15 µm Pycnidia: not observed Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: usually on rocks among mosses but occasionally on soil or tree bases World distribution: western, coastal North America Sonoran distribution: Arizona, southern California and Chihuahua. Notes: Leptogium californicum is most likely to be confused with L. lichenoides, that has more finely divided lobe tips (filiform) and usually a grayer, duller color. Within the Sonoran region L. californicum is more common in coastal regions, and L. lichenoides occurs at mid to high elevations at interior locations. The flattened lobes of L. californicum distinguish it from the upright lobes of L. corniculatum. Perhaps most problematic is to separate it from L. gelatinosum, which usually has broader lobes. Eventually it may prove to be only a form of L. gelatinosum with incised, instead of entire, rotund lobes. Its more shiny, revolute margin is similar to L. palmatum, but it is much smaller and flatter. More investigation is obviously needed to understand L. californicum and its variation.