Type: Paraguay. Distrito Capital: Asunción, Balanso, R. s.n. (G – lectotype, fide Hale 1965).
ATTENTION: The description below refers to the Galapagos specimens of Parmotremacf.mesotropum, not Parmotrema mesotropums.str. (see Notes below).
Description.Thallus corticolous; uppersurface whitish gray to ivory, dull to shiny, epruinose, emaculate, typically not cracked; lacking vegetative propagules; lobes moderate-sized to large, 5–10 mm wide, rotund, axils incised, margins eciliate; lowersurface with a very broad, distinct, pale brown, 3–6 mm wide, erhizinate marginal zone, the brown pigmentation becoming darker and eventually black towards the thallus center; rhizines short, slender, initially pale brown, darkening and eventually black towards the thallus center, mostly simple, rarely sparsely branched; medulla white. Apothecia and pycnidia not observed among the Galapagos specimens.
Chemistry. Cortex with atranorin [P+ yellow, K+ yellow, KC–, C–, UV–]; medulla with an unidentified substance (pale spot at Rf 30 in solvent C) [P–, K–, KC–, C–, UV–].
Ecology and distribution. Asia, North, Central and South America (Hale 1965; Divakar & Upreti 2005; Egan et al. 2016; Torres 2018). New for Ecuador and the Galapagos; only a single specimen known (from Volcán Darwin, Isabela).
Notes. The single specimen is here identified with some hesitation as P. cf. mesotropum. It is sterile and lacks both soredia and apothecia; unlike P. mesotropum s.str., this specimen does not contain caperatic and protolichesterinic acid, but instead we observed only a pale unidentified spot at Rf 30 in solvent C.