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DescriptionLife habit: lichenized; Thallus: adnate to loosely adnate, large foliose, lobate; lobes: usually subirregular to irregular, sometimes imbricate; apices: typically rotund, flat (to subconvex), ciliate or not; upper surface: gray or rarely yellow green, smooth, plane to rugulose, shiny or dull, sometimes white maculate, usually epruinose, epseudocyphellate, with or without soredia, isidia or pustules; upper cortex: pored epicortex, palisade plechenchymatous; medulla: usually white, sometimes pigmented in whole or part; cell walls: containing Cetraria-type lichenan; photobiont: primary one a Trebouxia, secondary photobiont absent; lower surface: black, broad brown (or mottled white and brown) zone peripherally, plane to sometimes wrinkled, attached by simple (rarely branched) rhizines, lacking tomentum; Ascomata: apothecial, laminal, orbicular, cup-shaped, pedicellate; margin: prominent, with thalloid rim; disc: imperforate or commonly perforate; exciple: gray or hyaline; epithecium: brown or brownish yellow; hypothecium hyaline; asci: lecanoral, apically with thickened wall layers and divergent axial body; apex: amyloid; 8-spored; ascospores: simple, ellipsoid, 8-35 x 5-18 µm (typically at the larger end of the range); wall: thick, hyaline; Conidiomata: pycnidial, laminal or marginal, immersed; conidia: sublageniform (3-10 x 1 µm) or filiform (8-20 x 1 µm); Secondary metabolites: some combination of orcinol depsides, orcinol depsidones, ß-orcinol depsides [and atranorin], ß-orcinol depsidones, (higher) aliphatic acids, pulvinic acid derivatives, anthraquinones, xanthones, and dibenzofurans [and usnic acids]; Geography: although cosmopolitan, predominately tropical,; Substrate: mostly on bark or acidic rocks, rarely on compacted soil.; Notes: Until the 1970s (Hale 1974) Parmotrema was usually treated as the section Amphigymnia of Parmelia, although it had been proposed as a separate genus over 100 years earlier. Nevertheless, it has received widespread acceptance in recent years. The circumscription given here follows Elix (1994h) and Hale, and is slightly less inclusive than the circumscription used by Krog and Swinscow (1981). Key characters for the genus include large thalli with broad, rotund lobe apices, broad naked marginal zones on the lower surface, frequent occurrence of marginal cilia, simple rhizines, thick-walled ellipsoid spores, and sublageniform or filiform conidia.