IUCN threat status:

Not evaluated

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Description

 Thallus: foliose, c. circular in outline, lobate; lobes: usually subirregular; tips: usually subrotund, eciliate; upper surface: pale yellow green to whitish or gray, smooth, plane to rugulose, dull, usually strongly pruinose, with or without soredia, emaculate; pseudocyphellae: absent; upper cortex: palisade plectenchymatous, pored epicortex; medulla: white, cell walls containing Cetraria-type lichenan; photobionts: primary one a Trebouxia, secondary photobiont absent; lower surface: ivory white to light brown or purplish black, velvety, frequently with a gray margin (like mouse fur), attachment by sparse, simple rhizines, cyphellae, pseudocyphellae and tomentum absent; Ascomata: apothecial, imperforate, laminal on thallus, orbicular, cup-shaped, sessile, margin prominent with thalloid rim; exciple gray or hyaline, hypothecium hyaline, epithecium brown or brownish yellow; asci: lecanoral, wall layers apex thickened, apex amyloid, with wide, axial body divergent towards apex; ascospores: c. 8 per ascus, simple, ellipsoid; 10-12 µm long, 4-6 µm wide; wall thin, hyaline; Conidiomata: absent or present, pycnidial, laminal, immersed; conidia: bifusiform, 6 x c. 1 µm; Secondary metabolites: upper cortex with usnic acid and atranorin and chloroatranorin; medulla with an orcinol depsidones and (higher) aliphatic acids; Geography: throughout arctic and northern boreal regions of the Northern Hemisphere and extending southwards in high montane areas; Substrate: mostly on non-calciferous rocks.; Notes: Among the Parmelia generic segregates, Arctoparmelia is most similar to the southern hemispheric Psiloparmelia in cortical chemistry and color of the lobe tips and the lower side, but the later genus has only a rudimentary epicortex, isolichenan in the cell walls and lacks rhizines. Among the yellow-green, non-pseudocyphellate parmelioids occurring in the Sonoran region, Flavoparmelia has broader lobes, larger spores, isolichenan in the cell walls and brown lobe tips on the lower side and the ubiquitous genus Xanthoparmelia has a shiny, epruinose upper surface, Xanthoparmelia-type lichenan in the cell walls, shiny brown or black lobe tips on the lower side, only usnic acid in the upper cortex and a far more complex medullary chemistry. 

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© Lichen Unlimited: Arizona State University, Tempe.

Source: Lichen Flora of the Greater Sonoran Desert Region

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