Thallus: crustose, effuse, not delimited, areolate to rimose-areolate, up to 0.3 mm thick but sometimes endolithic; prothallus: not observed areoles: +angular, plane to slightly verrucose, contiguous, 0.3-1 mm wide surface: clearly white (sometimes discolored pink on reddish rocks), smooth, sometimes dissolving in a granular to powdery crust, dull to slightly shiny, not discolored if wet cortex: not differentiated, consisting of discontinuous tissue up to 100 µm thick, containing numerous coarse crystal clusters, sometimes large crystals visible, medulla: thallus below algal layer becoming a discontinuous tissue; algal layer: 50-150 µm thick; algal cells: 6-16 µm in diam. Apothecia: frequent, adnate and slightly innate to sessile and constricted at base, +round to more often irregular in appearance, situated on areoles, scattered or in groups and than sometimes deformed, 0.3-1 mm in diam. disc: black-brown to black, paler (dark reddish brown) and +dark-spotted when wet, +concave to mostly plane, sometimes weakly convex, epruinose or with a weakly pruinose margin margin: thalline, white to grayish white, initially somewhat raised and relative thick, swollen, up to 0.2 mm wide, slightly flexuous, sometimes crenulate, persistent but becoming very thin, or rarely nearly excluded amphithecium: without a cortex or epinecral layer, with an algal layer filling almost the entire margin, up to 200 µm high and extending under the hypothecium, with a medulla consisting of discontinuous tissue filled with granular crystals parathecium: reddish brown, sometimes evident from above when wet, only developed toward the outer edge, thin, paraplectenchymatous, with conglutinated cells epihymenium: moderately brown to dark reddish brown, pigment [granules?] in places more strongly concentrated around the coherent groups of paraphyses so that the epihymenium appears spotty hymenium: hyaline, 40-60 µm tall; paraphyses 1.5-2.5 µm wide below, +coherent, slightly to strong swollen (clavate) and short-celled in the upper part, sometimes branched apically, up to c. 7 µm wide apically; hypothecium: hyaline, with intricate hyphae, up to 60-70 µm thick in center including subhymenium asci: narrowly clavate, Bacidia-type, 50-60 x 12-20 µm, 8-spored ascospores: hyaline, 1-septate, very rarely longer spores with 2- septate, ellipsoid to narrowly ellipsoid-fusiform, straight to sometimes curved, 12-20(-27) x 4-5 µm, thin-walled Pycnidia: immersed in the thallus, c. 120 µm in diam., irregularly round and dark brown above, hyaline below; conidiogenous cells: branched at base and elongate, 8-12 x 2-2.5 µm conidia: filiform, moderately to strong curved, 14-16 x 0.8 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on rather soft calcareous outcrops, and on soil World and Sonoran distribution: only known from San Nicolas Island in southern California at 15 and 150 m. Notes: Lecania chalcophila is distinguished by its completely white areolate thallus, that can disintegrate into a powdery tissue, and by its black apothecia with a weakly pruinose margin and epruinose discs. This new species resembles some morphs of L. turicensis, but that species never has a clearly white thallus. Furthermore, the thallus of L. turicensis, is more differentiated by having an epinecral layer, paraplectenchymatous tissue, and an algal layer without crystals clusters. Also its apothecia are pruinose and its ascospores are shorter. Lecania chalcophila and L. turicensis have been found together in one collection (T.H. Nash 38725), the former in the typical form and the latter with ±endolithic thallus with densely pruinose apothecia. The Weber L-88993 specimen was originally thought by us to be L. perproxima (Nyl.) Zahlbr., a species described from Illinois. However, the holotype of that species belongs to Caloplaca atroalba (Tuck.) Zahlbr.