Type: South Africa. Capeland: Kaprana, Cooper, P.J. 1813 (W – lectotype, H, M, UPS, US – isotypes, fide Sérusiaux 1984).
Description.Thallus saxicolous; upper surface whitish gray to ivory, dull to ± shiny, epruinose, emaculate, occasionally cracked, but not forming a distinctly reticulate pattern; abundantly sorediate; soralia marginal, linear to labriform (± crescent-shaped), or subcapitate; soredia ± granular, ± discolored by a brownish tinge, pale inside; lobes moderate-sized, 5–7(–10) mm wide, rotund, axils incised, margins sparsely ciliate; cilia short and slender, 0.4–2.5 mm long, black, mostly simple, very rarely branched; lowersurface often blackened throughout or becoming dark brown towards the margin or, especially below the soredia, often mottled white, typically with a distinct, 1–2 mm wide, erhizinate marginal zone; rhizines short, stout, black, simple to 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 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. Australia, India, Africa, Papua New Guinea, Mexico (Hale 1965; Sérusiaux 1984; Swinscow & Krog 1988; Elix 1994; Louwhoff & Elix 1999; Divakar & Upreti 2005; Egan et al. 2016). New for South America and the Galapagos; known from a single collection at the summit of Cerro Gavilan on Santiago Island, where the specimen was collected among ferns in sheltered crevices.
Notes. Superficially similar species are P. grayanum and P. rampoddense, but unlike P. cooperi, these two species do not contain lecanoric acid in their medulla. The medulla of P. grayanum contains no secondary metabolites and all spot tests are therefore negative. Parmotrema rampoddense contains alectoronic acid with α-collatolic acid and thus reacts KC+ rosé, quickly turning orange, and displays greenish blue fluorescence in ultraviolet light. Both P. grayanum and P. cooperi typically have sparse, relatively short cilia, and the lobes have a broadly erhizinate lower margin that is mottled white, brown and black. Parmotremarampoddense has abundant, very long and slender cilia, and the lobes are also broadly erhizinate below but lack the mottled appearance and instead are uniformly deep brown, gradually darkening towards the thallus center.