Type: Dominican Republic. Hispaniola: Soufrière Hills, Crater, Elliott, W.R. 114 (TUR – holotype, fide Hale 1965).
Description.Thallus corticolous; upper surface pale greenish yellow, dull, emaculate, smooth, not wrinkled, occasionally cracked, but not forming a distinctly reticulate pattern; abundantly sorediate; soralia marginal, linear to labriform, in parts becoming crowded, sublaminal and then increasingly capitate; soredia farinose to ± granular, typically concolorous with the thallus surface, not discolored, pale inside; lobes moderate-sized, (3–)7–10 mm wide, rotund, axils incised, margins eciliate (very rarely with few cilia); cilia, if present, stout, short, 0.3–0.5 mm long, black, mostly simple, rarely branched; lower surface with an erhizinate, ~ 1–2(–2.5) mm wide, deep brown margin, moderately to densely rhizinate and blackened towards the center; rhizines short, stout, black, simple to sparsely branched; medulla white. Apothecia and pycnidia not observed among the Galapagos specimens.
Chemistry. Cortex with both usnic acid and atranorin [P+ yellow, K+ yellow, KC–, C–, UV–]; medulla with protocetraric acid only [P+ yellow turning orange, K+ dirty yellowish brown, KC–, C–, UV–]; one analyzed specimen (Herrera-Campos, M.A. 10594, CDS 40331) additionally contains traces of echinocarpic acid [its medulla reacts KC± rosé to faintly orange].
Ecology and distribution. North, Central and South America, Africa, Hawaii (Hale 1965; Egan et al. 2016). First reported from the Galapagos by Weber (1981, 1986), subsequently by Elix & McCarthy (1998) and online (Bungartz et al. 2016). A common species, particularly throughout the coastal zone and dry zone, less abundant in the transition zone, only very rarely found in the humid zone; most specimens grow on bark, few on rock, typically in sunny, wind- and rain-exposed, less frequently ± shaded and sheltered habitats; most commonly found on Bursera or generally dry zone vegetation, i.e., Erythrina or Zanthoxyllum trees, Croton scrub and cacti (Jasminocereus, Opuntia), along the coast also in mangroves (Laguncularia, Hippomane); one specimen was collected in the agricultural area of Santa Cruz, on Cedrela.
Notes. For differences from the newly described P. lawreyi, see the description there.