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, 3-25 cm in diam., lobate lobes: subirregular, elongate, becoming somewhat imbricate, plane, separate, 8-20 mm wide; apices: rotund, eciliate upper surface: gray, smooth to rugulose, dull, emaculate, becoming reticulately cracked with age; soredia, isidia and pustulae: absent medulla: white with continuous algal layer lower surface: black with brown naked zone peripherally, centrally rhizinate; rhizines: scattered, simple, black Apothecia: common, substipitate, up to 10 mm in diam.; margin: crenulate, emaculate; disc: brown, perforate ascospores: ellipsoid, 28-32 x 14-16 µm Pycnidia: not seen Spot tests: upper cortex K+ yellow, C-, KC-, P-; medulla K+ yellow turning deep red, C-, KC-, P+ orange Secondary metabolites: upper cortex with atranorin and chloroatranorin; medulla with salazinic acid (major) and consalazinic acids (minor). Substrate and ecology: montane usually on trees in open habitats World distribution: neotropics and India Sonoran distribution: Sonora, in the Sierra Madre Occidental.
Type: Jamaica. [State or Province and exact locality, and collector unknown], s.c., (G – lectotype!, designated by Hale 1965).
Description.Thallus corticolous, rarely saxicolous; uppersurface whitish gray to ivory, shiny to ± dull, epruinose, emaculate, not cracked, but older parts ± wrinkled; lacking vegetative propagules; lobes moderate-sized to large, 4–12 mm wide, ± rotund, eciliate, distinctly delimited along the lobe edge by a conspicuous black rim; lowersurface with a broad, pale to deep brown erhizinate, ~ 3–5(–7) mm wide margin, blackening and sparsely rhizinate towards the thallus center; rhizines short, stout, black, mostly simple, rarely sparsely branched, often clustered in groups, with erhizinate areas in between; medulla white. Apothecia absent, or rare to moderately abundant, 0.5–9 mm in diam., with a cupulate thalline margin, disc pale brown, deeply concave, imperforate; asci clavate, Lecanora-type, ascospores 8/ascus, simple, broadly ellipsoid, (25.7–)27.8–34.1(–34.7) × (14.9–)15.7–17.3(–17.8) μm (n = 25), very thick-walled (~ 2–3 μm thick). Pycnidia not observed in the Galapagos (the lectotype according to Spielmann 2009 has abundant, conspicuous pycnidia with a black ostiole and sublageniform conidia, 6–8 × ~ 1.0 μm).
Chemistry. Cortex with atranorin [P+ yellow, K+ yellow, KC–, C–, UV–]; medulla with salazinic acid [P+ deep yellow, K+ yellow, soon turning blood-red, KC–, C–, UV–].
Ecology and distribution. Asia (Hale 1965; Divakar & Upreti 2005), North, Central and South America (Hale 1965; Fleig & Riquelme 1991; Egan et al. 2016); cited from continental Ecuador by Cevallos Solórzano (2012). From Galapagos previously reported only online (Bungartz et al. 2016); only one recent and one historical specimen collected, both from the transition zone of San Cristóbal Island.
Notes. In Galapagos, P. latissimum is one of only three species found without vegetative propagules. Superficially it is most similar to P. mesotropum, which also has broad, rotund lobes, typically growing on bark, but that species lacks salazinic acid and medullary spot test reactions are all negative. Most specimens of P. latissimum are corticolous and thus easily distinguished from the exclusively saxicolous P. eborinum. Parmotrema eborinum generally has much smaller lobes (see description) that are densely lobulate; its medulla contains protocetraric instead of salazinic acid.