Life 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 1970’s (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.
Life habit: lichenized Thallus: foliose, 4-20 cm wide, loosely adnate to adnate, lobate lobes: irregular to sublinear, broad, 3-30 mm wide, often lacinate, elongate; apices: usually subrotund to rotund, ciliate (absent in one species); cilia: sparse to dense, simple to sparsely branched, not bulbate upper surface: gray to dark gray, gray-green or pale green, conspicuously effigurate-maculate forming an intricate reticulate network, becoming cracked along the maculae but lacking true pseudocyphellae, pruinose or not towards the tips; with or without soredia or isidia upper cortex: pored epicortex, vaulted paraplectenchymatous, medulla: white, relatively thick, hard and chalky, cell walls containing an intermediate type of lichenan photobionts: primary one a Trebouxia, seconddary photobiont absent lower surface: glossy black centrally, brown peripherally, plane to papillate marginally, rhizinate; rhizines: simple but becoming sometimes squarrose, short ones throughout and longer ones in tufted groups; cyphellae, pseudocyphellae and tomentum absent Ascomata: apothecial, becoming perforate, laminal, orbicular, cup-shaped, substipitate, perforate or imperforate; margin: prominent with thalloid rim, ciliate; exciple: gray or hyaline; epithecium: brown or brownish yellow; hypothecium: hyaline asci: lecanoral, apex thickened and amyloid, with wide, axial body divergent towards apex, c. 8-spored ascospores: simple, ellipsoid to broadly ellipsoid, 10-18 x 6-11 µm; wall: thin, hyaline Conidiomata: pycnidial, laminal, immersed, punctiform conidia: cylindrical to filiform, 9-16 x 1-1.5 µm Secondary metabolites: upper cortex with atranorin and chloroatranorin; medulla with some combination of orcinol or beta-orcinol depsidones, beta-orcinol depsides, a xanthone or aliphatic acids Geography: cosmopolitan with a major center in South America, temperate to tropical forests and woodlands Substrate: mostly on bark, sometimes on acidic rock. Notes: Rimelia is a segregate from Parmotrema that was initially recognized as a distinct group by Vainio in 1890, who later raised it to a sectional level [sect. Irregulares (Vainio 1923)]. The reticulate network of maculae on the upper suface is probably its most distinctive feature, which Parmotrema lacks. Parmotrema also does not have as well developed cracks in the upper cortex and has shorter, sublageniform conidia.