Life habit: lichenized Thallus: foliose, appressed but loosely adnate, up to 3 or 4 cm in diameter, but somewhat difficult to measure in the irregular, often non-rosette forming thallus lobes: 1-3 mm broad, ± flat to irregularly concave, rounded and irregularly overlapping to somewhat elongate; 120-180 µm thick, upper cortex distinctly paraplectenchymatous, 17-40 µm thick, lower cortex irregularly prosoplectenchymatous, 12-35 µm thick, in part intergrading with and poorly delimited from the medulla upper surface: gray (distinctly green when wet!), usually with a bluish tint, especially in younger areas, darkening with a bluish to greenish tint in older central areas, the entire upper surface evenly to somewhat unevenly pruinose, mostly smooth on the lobes and only slightly roughened or cracked inwardly soredia: granular (25-50 µm diam.), bluish-gray, in small soralia (0.5-1.5 mm); soralia: marginal first and then also laminal in older regions, rounded on the lamina, rounded to irregular on the margins medulla: white photobiont: primary one a Trebouxia, secondary photobiont absent lower surface: mostly pale, white to slightly tan, peripheral areas with a conspicuous broad region on the lobes with the same bluish pigment as the upper cortex (and the same spot tests, below), older parts often becoming darkened (necrotically), sometimes to almost black; moderately rhizinate (but rhizines not evenly distributed, sparse to rather abundant in different areas), the rhizines simple to irregularly furcate, up to 0.5-1 mm long, concolorous with the lower surface Ascomata: not seen (but one apothecium reportedly seen by Moberg 1980b) Conidiomata: pycnidial, rare conidia: ± cylindrical to weakly fusiform (faintly wider in the middle), 5-6.5 x 1µm Spot tests: bluish-greenish regions (of both the upper and lower cortex) are K+ rose-violet, C+ faint but quickly bleaching, N+ rose (fading somewhat); medulla K-, C-, KC-, P- Secondary metabolites: none detected. Substrate: in the study area known only on acidic rock World distribution: Arizona, Peru, Africa, Saudi Arabia, Tasmania Sonoran distribution: known only from several sites in the Mount Baldy Wilderness Area in east-central Arizona, above 2900 m. Notes: Based on the characters of the single observed apothecium, Moberg (1980b) placed this species in Pyxine, but noted that its pale lower surface, lack of secondary chemistry, and bluish pigmentation were unique for that genus. He did not find pycnidia (present however in Krog 3K18/110 from Kenya), and therefore did not observe that the conidia of this species are larger (5-6.5 µm vs. 3-4 µm) and different in shape (cylindrical to weakly fusiform vs. bacilliform to weakly bifusiform) than other species of Pyxine. Regardless of the apothecial or spore types, this list of distinctions seems to me sufficient basis for separation of C. nubila from Pyxine. This unusual species is more likely to be identified as a species of Physconia, primarily because of its darkened and K- (or at least not yellow) upper cortex and its distinctive pruina. However, the unusual bluish or greenish gray pigments (K+ rose-violet) found in both the upper and lower cortex, and the mostly pale lower surface with simple or sparsely furcate rhizines, will clearly distinguish Culbersonia from all species of Physconia as well as all other foliose species in the area.