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Common Names: The Icelandmoss Lichens (and others). Several are assigned to this genus, reflecting its very heterogeneous circumscription: “Brown” is applied to two species (C. commixta and C. hepatizon), stressing their surface colour and, more importantly, their generic similarity with other lichens of that name (i.e., members of Melanelia and Neofuscelia). “Icelandmoss” is the traditional name given to Cetraria islandica and its allies. “Paperdoll” is a fanciful name applied to two species (C. cucullata and C. nivalis), referring to their pale, upright, “cut-out” lobes. “Ruffle” is applied to several species, describing their typically wrinkled upper surface. “Thornbush” is applied to two species (C. californica and C. merrillii), conveying their spiny, shrub-like habit.
Small to large stratified foliose lichens, corticate above and below, sorediate or not, lobes rather closely appressed to semi-erect or erect, short to more often elongate, averaging to 0.5–10 (–12) mm wide, thin to somewhat thick, occasionally bearing protruberant marginal pycnidia or cilia. Upper surface brownish, blackish, or brightly coloured; lower surface coloured alike with upper surface, often lacking rhizines. Medulla white (rarely yellow). Photobiont green.
Apothecia located along lobe margins, disc brown or black; spores simple, spherical or ellipsoid, colourless, 8 per ascus.
Notes: Thirty-eight species of Cetraria are reported for North America. Nineteen of these occur in B.C. As presently delimited, Cetraria is a heterogeneous genus. Although several species groups are segregated from it as distinct genera (e.g. Asahinea, Cetrelia, Esslingeriana, Masonhalea, Platismatia and Vulpicida), a number of other species and species groups also deserve generic rank. Recently Hale (1987) transfered some of these to Tuckermannopsis. This disposition, however, seems more nomenclatural than taxonomic and is not followed here. Also not accepted here (pending further study) is the separate genus Allocetraria (Randlane and Saag 1992).
Upper surface essentially dark: olive-green, brown or blackish AND
Soredia absent; true isidia also absent AND
Growing over bark, wood, earth or humus AND
Over trees and shrubs; pseudocyphellae absent over lower surface; lobes short to occasionally elongate, margins usually even (i.e., lacking short projections, though marginal cilia may be present) AND
Lobes pale olive-green to dark brown, sparsely to moderately branched, but never finely dissected or shrub-like AND
Lobe margins naked or at most bearing very short cilia, these averaging to 1 mm long; medulla KC- AND
Lobes generally averaging to 1–5 mm wide at maturity; lower surface generally distinctly paler than upper surface; apothecia frequently dominating lobes; medulla white (and K-) throughout AND
Thallus mat-forming to rarely cushion-forming, averaging to 3–7 cm across at maturity (Note: some forms can be smaller); upper surface wrinkled at maturity; pycnidia generally numerous; over deciduous and coniferous trees
Cortex KC+ yellow or apparently KC-.
Caperatic and usnic acids and an unknown fatty acid.
Source: Lichens of British Columbia