Diagnosis: Differs from P. cristiferum by the abundant and conspicuous, long, slender, typically erect cilia along the lobe margins (± perpendicular to the lobe), and by the overall darker, mostly blackened lower side, only a narrow dark brown marginal zone that is not mottled white.
Type: Ecuador. Galápagos: Isla Santa Cruz, vicinity of Academy Bay, just N of Research Station, dry zone, below barranco, on huge boulder of a talus slope, 15-Feb-1964, Weber, W.A. 403 (L-40540, COLO 192658 – holotype!).
Description.Thallus saxicolous; upper surface whitish gray to ivory, shiny to ± dull, epruinose, emaculate, but in parts irregularly cracked; abundantly sorediate; soralia marginal, linear to labriform (± crescent-shaped); soredia farinose, ± concolorous with the thallus surface, in parts typically discolored by a brownish or dark grayish tinge, pale inside; lobes broad, small to moderate-sized, 2–6(–7) mm wide, ± rotund, axils incised, margins ciliate, distinctly delimited along the lobe edge by a conspicuous black rim; cilia long, stout and slender, 0.5–1(–1.5) mm long, black, mostly simple, very rarely branched, typically erect (± perpendicular to the lobe surface); lower surface with a narrow, erhizinate, 0.5–1 mm wide area, overall blackened throughout or with a very narrow, dark brown margin; rhizines short, stout, black, mostly simple; medulla white. Apothecia and pycnidia not observed among the Galapagos specimens.
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–].
Etymology. Named for its long, conspicuously erect cilia.
Ecology and distribution. Endemic to the Galapagos, known only from the type.
Notes. At first glance similar to P. cristiferum, although its equally broad lobes are abundantly ciliate, with long, stout and slender cilia. The species is further distinguished by a lower surface that is almost entirely blackened throughout and only in a narrow part along the lower lobe edge might not be pitch black, but dark brown. Generally, the black to deep brown pigmentation of the lower side extends all the way to the margin and is therefore visible from above – the lobes appearing delimited by a distinct black to dark brown edge.