Thallus: foliose, up to 3.5(-5) cm in diam., usually +orbicular lobes: linear-elongate to somewhat shorter and rounded, 0.5-1.5(-3) mm broad, flat to weakly concave, prostrate upper surface: brown to reddish-brown, more or less smooth to weakly papillate, epruinose, dull or more often weakly shiny, with a +conspicuous, minutely roughened whitish pseudocyphellae bordering the lobes, without soredia or isidia upper cortex: paraplectenchymatous medulla: white lower cortex: paraplectenchymatous lower surface: pale tan (occasionally almost white) to pale brown, dull; rhizines: sparse, simple, concolorous with the lower surface or darkening Apothecia: frequent, up to 2.5(-4) mm in diam.; margin: becoming crenate-papillate, bearing pseudocyphellae on the papillae ascospores: broadly ellipsoid, 6-9 x 4-6 µm Spot tests: cortex all spot tests negative, medulla C+ red or C-, KC+ rose-red Secondary metabolites: olivetoric acid or physodic acid. Substrate and ecology: on bark (usually pine), less often on old wood World distribution: southwestern North America Sonoran distribution: mountains of Arizona and northernmost Baja California. Notes: Tuckermanella weberi frequently occurs in mixed collections with T. fendleri, but the brown color and usually conspicuous marginal pseudocyphellae make it easy to distinguish from that species. It is the only species of Tuckermanella with such distinctive spot tests, being either C+ rose-red (olivetoric acid) or C- and KC+ rose red (physodic acid). Tuckermanella arizonica (and some other fatty-acid containing species of Tuckermanella and Tuckermannopsis) sometimes gives a weak KC+ yellowish reaction, but this is very different and much weaker than the KC+ reaction caused by physodic acid.