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DescriptionThallus: crustose, leprose, unstratified or, in thick specimens, sometimes indistinctly stratified, indeterminate, thin, irregularly spreading, sometimes forming scattered granules, but usually ±continuous; surface: bright yellow throughout, often with an orange or greenish tinge, composed of a mass of fine soredia, 12-30(-40) µm in diam.; medulla: usually not evident, in thick thalli sometimes indistinctly present, yellow; Ascomata: rare (in the Sonoran region, known from one specimen from Mexico), up to 0.5 mm in diam., ±superficial; disc: pale orange, often yellow-pruinose; margin: thin, ecorticate, soon becoming excluded; exciple: poorly developed, composed of anastomosing hyphae; epihymenium: hyaline, up to 18 µm tall, composed of of a reticulate layer of richly branched paraphysoids; hymenium: hyaline, up to 50 µm tall (including epihymenium); paraphysoides: 1-1.5 µm wide, richly intertwined in epihymenium; hypothecium: colorless, poorly developed; asci: clavate, 8-spored; ascospores: 9-14 x 3 µm; Spot tests: K- or K+ orange, sometimes darkening to red-black, C-, KC-, P- or P+ orange; UV+ dull orange or UV-; Secondary metabolites: calycin and/or pinastric acid.; Substrate and ecology: on bark, wood, stone (mainly rhyolite) in dry and shaded microhabitats; World distribution: cosmopolitan except for arctic-alpine and antarctic areas; Sonoran distribution: coastal California, Arizona, Baja California Sur, Baja California, Chihuahua, Sonora at 1-2550 m.; Note: Psilolechia lucida (Ach.) M. Choisy, another unstratified, totally leprose species, is distinct, e.g., by the production of rhizocarpic acid; reports of the species from the Sonoran region have not been substantiated.