Description.Thallus corticolous, lignicolous, less frequently saxicolous; upper surface whitish gray to ivory, shiny to ± dull, epruinose, emaculate, not cracked; abundantly isidiate; isidia laminal, irregularly spread across the thallus surface, cylindrical, simple to sparsely branched, brown to blackened at their tip, eciliate; lobes broad, moderate-sized to large, 0.8–10(–14) mm wide, ± rotund, axils incised, margins eciliate; lower surface with a broad, pale to deep brown, erhizinate, ~4–6 mm wide margin, blackening and sparsely rhizinate towards the thallus center; rhizines short, stout, black, mostly simple, rarely sparsely branched, often growing in clusters; medulla white. Apothecia often absent, but occasionally observed, 0.2–9 mm in diam., with a cupulate thalline margin, disc dark brown, deeply concave, imperforate; asci clavate, Lecanora-type, ascospores 8/ascus, simple, broadly ellipsoid, (12.9–)13.6–15.3(–15.8) × (6.4–)6.8–8.0(–8.4)μm (n = 25), thick-walled (~ 1 μm thick). Pycnidia not observed among the Galapagos specimens; conidia according to Swinscow & Krog (1988) filiform, 12–16 μm long.
Chemistry. Cortex with atranorin [P+ yellow, K+ yellow, KC–, C–, UV–]; medulla with lecanoric acid [P–, K–, C+/KC+ bright red (C and KC reactions are evanescent and must be examined under continuous observation); UV–].
Ecology and distribution. Cosmopolitan; reported from Oceania, Asia, Africa, Europe, North, Central and South America (Hale 1965; Awasthi 1976; Swinscow & Krog 1988; Purvis et al. 1992; Elix 1994; Malcolm & Galloway 1997; Louwhoff & Elix 1999; Kurokawa & Lai 2001; Benatti & Marcelli 2009; Spielmann & Marcelli 2009; Egan et al. 2016), including continental Ecuador (Cevallos Solórzano 2012). First reported from the Galapagos by Dodge (1936), subsequently by Weber (1966, 1981, 1986), Elix & McCarthy (1998) and online (Bungartz et al. 2016). Possibly the most common species of Parmotrema in the Galapagos; from the coastal zone all the way to the high-altitude dry zone, most common in the dry zone and transition zone, followed by the humid zone; most frequently on bark of native trees (Bursera, Cordia, Piscidia, Pisonia, Erythrina, Zanthoxylum) and shrubs (Clerodendrum, Croton), occasionally on wood or cacti (Jasminocereus, Opuntia), also in mangroves (Conocarpus, Hippomane), rarely on introduced trees of the agricultural areas (Cedrela), common also on rock; mostly at sunny and exposed, less frequently ± shaded and sheltered sites.
Notes. For differences from the similar P. endosulphureum and the exclusively saxicolous P. pustulotinctum, refer to the descriptions of these species.
Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.
Thallus: foliose, loosely adnate, 3-30 cm in diam., lobate lobes: subirregular, elongate, slightly imbricate, plane, separate, 10-20 mm wide; apices: rotund, becoming crenate and dissected with age, ciliate; cilia: up to 2.0 mm long upper surface: gray, smooth, dull centrally, shiny marginally, emaculate, finely reticulately cracked with age isidia: simple to coralloid branched, frequently very dense, sometimes apically ciliate, common, laminal to marginal; soredia and pustulae: absent medulla: white with continuous algal layer lower surface: black with brown naked zone peripherally, centrally rhizinate; rhizines: simple Apothecia: rare, substipitate, up to 8 mm in diam.; margin: sparsely isidiate; disc: brown, usually imperforate ascospores: ellipsoid to broadly ellipsoid, 13-16 x 7-10 µm Pycnidia: rare, punctiform conidia: filiform, 12-16 x 1 µm Spot tests: upper cortex K+ yellow, C-, KC-, P-; medulla K-, C+ red, KC+ red, P- Secondary metabolites: upper cortex with atranorin and chloroatranorin; medulla with lecanoric acid (major), orsellinic acid (trace). Substrate and ecology: usually on trees in open habitats, rarely on rocks World distribution: pantropical and adjacent temperate regions Sonoran distribution: coastal plain to mountains of southern Baja California Sur and Sinaloa.