Diagnosis. Differs from P. dominicanum by the presence of coralloid to cauliflower-like isidia that rupture to release soredia.
Type: Ecuador. Galápagos: Isla San Cristóbal, northwestern foothills of Media Luna, inland from the NW-coast, 0°43′41″S, 89°18′44″W, 75 m alt., dry zone, open woodland of Cordialutea and Burseragraveolens, on NE-exposed trunk of Burseragraveolens (~ 20 cm in diam.), semi-shaded, ± wind- and rain-sheltered, 22-Apr-2007, Bungartz, F. 6187 (CDS 34399 – holotype!).
Description.Thallus corticolous; uppersurface pale greenish yellow, dull, emaculate, smooth, not wrinkled, occasionally cracked, but not forming a distinctly reticulate pattern; pustulate-isidiate, rupturing into soralia; isidia submarginal to laminal, very variable, initially cylindrical to dactyliform (constricted at their base, apically tapering), sometimes ± flattened and almost squamulose-lobulate, with age increasingly branched, becoming coralloid to cauliflower-shaped and then rupturing into coarse, granular, ± pseudocorticate soredia; 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–.05 mm long, black, mostly simple, rarely branched; lowersurface with a 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–].
Etymology. Named in honor of our good friend and colleague James D. Lawrey, to whom this publication is dedicated on the occasion of his 70th birthday.
Ecology and distribution. Endemic to the Galapagos; known from a few collections in the dry zone of Floreana, San Cristobal and Volcán Alcedo; all specimens collected on bark of Bursera graveolens, both in sunny, exposed and ± shaded and sheltered habitats.
Notes. The pustular, initially cylindrical isidia that soon develop into large, cauliflower-shaped clusters, breaking apart into coarse granular soredia, distinguish this species from the much more common P. dominicanum.