Thallus: lacking or inconspicuous (best seen after wetting), rimose; prothallus: inconspicuous to indiscernible surface: if present, white, esorediate medulla: white, I- Apothecia: black, with distinctly constricted base, up to 2.4 mm in diam. disc: black, epruinose to slightly pruinose, flat to moderately convex margin: black, persistent for a long time, dull to shiny exciple: with a blackish green epihymenium-like rim, unpigmented inside but at least marginally opaque ochre due to crystalline masses, 40-90 µm wide epihymenium: bright green to olive green, c. 15 µm thick hymenium: hyaline, 50-70 µm tall; paraphyses: rarely branched and anastomosing subhymenium: hyaline or faintly green, 40-70 µm thick hypothecium: faintly ochre (almost unpigmented) asci: clavate, 40-60 µm, 8-spored ascospores: hyaline, simple, ellipsoid to oblong-ellipsoid to narrow oblong, (9.5-)12.5-15(-20) x (3.5-)3.8-6(-7) µm, length-width-index 2.4-3.9 Pycnidia: immersed conidia: cylindrical, 6-11 x 1-1.3 µm [studied in 2 specimen] Spot tests: cortex and medulla K-, C-, KC-, P- Secondary metabolites: [not known; specimens usually too small for TLC]. Substrate and ecology: on non-calcareous pebbles and rock chips in the lower montane zone World and Sonoran distribution: only known in a few collections from Arizona and southern California; very rare in the lower montane zones. Note: Lecidea cruciaria is a rather critical and insufficiently known taxon, that might be rather near to Lecidea plana. Its epithet refers to its type locality Santa Cruz Island in southern California.