Thallus: composed of small convex areoles developing into lobate squamules squamules: appressed to ascending, rounded in outline or weakly to moderately incised or lobate, up to 0.6 mm long and 0.5 mm wide, scattered to crowded to imbricate, sometimes forming thick cushions upper surface: mostly green yellow, sometimes yellow to orange yellow in parts, mostly "pruinose" upper cortex: pseudoparenchymatous, 7-15 µm thick lower cortex: , similar to the upper cortex but thicker, 10-25 µm thick Apothecia: common, lecanorine, 0.3-0.8 mm wide disc: darker yellow than the thallus, round, ±flat margin: thick, entire to somewhat crenate, concolorous with the thallus exciple: thin, not or only faintly visible from the outside epihymenium: yellow-brown hymenium: hyaline, 60-80 µm tall; paraphyses: simple, cylindrical or with somewhat swollen tips; hypothecium: hyaline asci: clavate, 8-spored ascospores: hyaline, simple to 1-septate, ovoid to citriform or teardrop-shaped, the majority of the spores have one or both ends pointed or at least attenuate, 10-15.5 x 5.5-7 µm Pycnidia: common, appearing as yellow-orange warts on the squamules conidia: hyaline, ellipsoid, 3-4 x 1.5-2 µm Spot tests: K- to K+ reddish, KC-, C- Secondary metabolites: calycin, pulvinic acid, pulvinic dilactone and vulpinic acid. Substrate and ecology: over calcium-free rocks but mostly not directly on the rock but on soil in crevices, on mosses or on other lichens, occasionally also on bark World distribution: southwestern North America, north to at least, Utah and Colorado Sonoran distribution: widespread throughout the region in Arizona, southern California, and Baja California. Notes: Candelariella citrina is a very common species in the southwestern parts of North America but has usually been identified as C. rosulans in the herbaria. It is charatcerized by its short spores, that have one or both ends pointed. The thallus is variable in color and shape but often characteristic with greenish squamules with a coarse "pruinose" surface. Frequently it grows together in mixed stands with C. rosulans, C. "complanata" and Candelina submexicana. Candelariella terrigena, a younger synonym to C. citrina (Westberg in prep.), has been a misunderstood name applied to various material growing on soil.