Thallus: squamulose squamules: up to 1.5 mm diam., concave to plane, deeply lobed, usually with the major part of the underside free from the substrate upper surface: light green to light brown, more or less pruinose towards the lobe tips; margins: not thickened; vegetative diaspores: absent upper cortex: up to 45 µm thick, composed of anticlinally oriented hyphae covered by crystals which are, at least partly, insoluable in K, containing scattered remnants of algae (chlor-zinc-iodine!), with a thin epinecral layer medulla: containing crystals which are, at least partly, not dissolving in K, I+ faintly blue algal layer: continuous lower cortex: poorly developed lower surface: whitish; rhizines absent hypothallus: absent Apothecia: up to 1 mm diam., more or less immersed when young, becoming sessile and often constricted at the base, plane and marginate when young, becoming more or less convex and immarginate, medium to dark brown, pruinose ascospores: ellipsoid, 1-septate, hyaline, 9-12 x 3.5-5 µm Pycnidia: immersed conidia: shortly bacilliform, 3-4 x c. 1 µm Spot tests: K-, C-, KC-, P+ orange (medulla) or P- (cortex) Secondary metabolites: pannarin, zeorin, and un-determined secondary products. Substrate and ecology: on or among cyanolichens on a steep to overhanging rock face, in Madrean oak-pine forest at 1800 m (single locality) World and Sonoran distribution: Barranca del Cobre, Chihuahua. Notes: Solenopsora chihuahuana has flattened to concave squamules in contrast to the convex squamules of S. crenata, and the spores of S. chihuahuana are substantially shorter than those of S. crenata. Neither of the species are as brittle as the upright S. cladonioides (below).