Type: India. Tamil Nadu: Nilgiri Mountains [as ‘Nilgherries’], Coonoor, Gray, M.C. 1893 (P – holotype, fide Hale 1965).
Description.Thallus saxicolous; uppersurface white to whitish gray, 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, typically discolored by a dark gray tinge, pale inside; lobes moderate-sized, 5–7(–10) mm wide, rotund, axils incised, margins sparsely ciliate; cilia short and slender, 0.1–2.5 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(–2.5) 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 protolichesterinic acid [P–, K–, KC–, C–, UV–].
Ecology and distribution. Africa, Asia, Oceania, North and South America (Hale 1965; Swinscow & Krog 1988; Chen et al. 2005; Jungbluth 2006). New for Ecuador; from the Galapagos previously reported only online (Bungartz et al. 2016); only rarely found, on exposed rock, in the transition zone and humid zone.
Notes. This saxicolous species closely resembles both P. praesorediosum and P. mordenii but it is distinctly ciliate along its lobe margin and does contain protolichesterinic acid in its medulla.