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DescriptionLife habit: lichenized; Thallus: foliose, irregularly circular to elongate, 10-30 cm wide but sometimes covering much larger patches of substrate, often lacunose, loosely adnate, lobate; lobes: irregular, often dichotomously branched, 2-10 mm wide, elongate, lobe tips usually subtruncate to truncate, entire, crenulate or with small lobules (phyllidia), eciliate; upper surface: yellowish green, medium to dark brown, shiny or very slightly pubescent, smooth, flat or wrinkled, sometimes with prominent depressions with a network of ridges; with or without soredia or isidia; cyphellae and pseudocyphellae absent; maculae absent; upper cortex: paraplectenchymatous; medulla: white, lax or compact; photobionts: primary one a chlorococcoid green (Myrmecia or Trebouxia) or a cyanobacterium (Nostoc); secondary one (Nostoc) present in internal or external cephalodia in green algal dominant species; lower cortex: paraplectenchymatous; lower surface: pale brown to yellow-brown, often rugulose, tomentose, rhizinate; rhizines simple to squarrose; pseudocyphellae and cyphellae absent; Apothecia: rather rare, orbicular, cup-shaped, sessile to substipitate; disc: brown or dark red; hemiangiocarpous ascomata development; margin: prominent with thalloid rim; exciple: hyaline or light brown, 20-30 µm thick; epihymenium: brown or brownish yellow; hymenium: hyaline, I+ blue; hypothecium: hyaline; asci: clavate, Peltigera-type, 8-spored; ascospores: fusiform to accicular, colorless to pale brown, 1-7-septate; Conidiomata: pycnidial, laminal, immersed, punctiform, area around ostiole black; conidia: +cylindrical-elongated to bifusiform, 4-5 x 1-2 µm; Spot tests: upper cortex K-, C-, KC-, P-; medulla K+ pale yellow or K-, C-, KC-, P-; Secondary metabolites: upper cortex with or without usnic acid, medulla with some combination of ß-orcinol depsides or depsidones, triterpenes; Geography: world-wide in arctic regions and moist forests of North and South America, Eurasia and Australasia; Substrate: commonly on trees, occasionally on rocks or soil.; Notes: Lobaria and Durietzia do not have pseudocyphellae or cyphellae on their lower surfaces, but Sticta has cyphellae and Pseudocyphellaria has pseudocyphellae on their lower surfaces. Durietzia has either maculae or pseudocyphellae present on its upper surface, while Lobaria does not have either on its upper surface. The present concept of the genus Lobaria is still an artificial one. The section Ricasolia has a flat thallus, while section Lobaria has a distinctly lacunose thallus. Section Lobaria includes the Lobaria retigera group (containing cyanobacteria), but not Lobarina scrobiculata (Scop.) Nyl. ex Crombie. The genus Lobarina (Vain.) Nyl. ex Cromb. has a denuded portion of lower surface of lobes composed of periclinal hyphae, while species of Lobaria has screlo- or paraplectencymatous hyphal tissue in the lower cortex.