Thallus: foliose, up to 5(-7) cm in diam., usually +orbicular lobes: somewhat elongate but branched and partly contiguous, 0.6-1.2 mm broad, flat to weakly concave, prostrate upper surface: tan-brown to brown, sometimes with a slight reddish brown or olive-brown cast on lobe ends, +smooth at the periphery but becoming irregularly rugose and sometimes foliolate inward, the lobe edges bordered with distinctive whitish pseudocyphellae, epruinose, weakly shiny at the periphery, dull inward, without soredia or isidia upper cortex: paraplectenchymatous medulla: white in part, partly to totally off-white to pale ochre-yellow lower cortex: paraplectenchymatous lower surface: pale to darker tan or almost brown in oldest parts, smooth to weakly rugose, dull; rhizines: sparse, simple, concolorous with the lower surface or darkening Apothecia: infrequent, up to 3 mm in diam.; margin: crenate to papillate, bearing pseudocyphellae on the crenae or papillae ascospores: ellipsoid, 7-9.5 x 5-5.5 Ám Pycnidia: black, immersed to weakly emergent, mostly submarginal and laminal Conidia: bifusiform, 4-6 x 1 Ám Spot tests: cortex all spot tests negative, medulla P-, K+ pale to darker violet or K- in pure white parts, C- Secondary metabolites: caperatic acid and an unidentified quinonoid pigment. Substrate and ecology: on wood (or bark?) of conifers World distribution: northern Mexico Sonoran distribution: Chihuahua. Notes: The brown color and distinctive marginal pseudocyphellae on the lobe margins of Tuckermanella pseudoweberi are much like T. weberi, but T. pseudoweberi is larger and has a very different chemistry, producing caperatic acid (and a quinonoid pigment) instead of olivetoric acid or physodic acid.