Diagnosis. Similar to Parmotremaclavuliferum but exclusively saxicolous, clavulae white below, but speckled with black, lobes abundantly ciliate and generally much smaller, their lower side lacking a distinct erhizinate margin; unlike fertile P. herrei with shorter, simple cilia, and reproducing with soredia.
Type: Ecuador. Galápagos: Isla Floreana, Cerro Ventanas, top and upper slope at southern point of the ridge, 1°16′25.89″S, 90°25′42.20″W, 424 m alt., transition zone, lower transition zone; low vegetation of Lecocarpuspinnatifidus and some Macraealaricifolia shrubs, much open ground with small lava pebbles, overgrowing pebbles on the ground, sunny, wind and rain-exposed, 18-Jan-2011, Bungartz, F. 9881 (CDS 47219 – holotype!, CGMS – isotype!).
Description.Thallus saxicolous; uppersurface white to whitish gray, dull to shiny, epruinose, densely reticulate-maculate, often cracked; abundantly sorediate; soralia capitate, conspicuously stalked, at the tip of distinct, short to elongate, laciniate lobes (clavulae); soredia ± granular, surface creamy white, typically not discolored; lobes small, narrow, 0.5–2(–2.5) mm wide, ± angular, abundantly ciliate; cilia short and slender, 0.3–1 mm long, black, mostly simple, very rarely branched; lowersurface blackened throughout or strongly dark brown at the very edge of the lobes, the rhizines growing all the way to the edge of the lobe, lacking a distinct deep brown erhizinate lower margin, the lower cortex occasionally in parts mottled white (especially below the clavulae); rhizines, where present, long, slender, black, mostly simple, rarely sparsely branched; medulla white. Apothecia not observed among Galapagos specimens. Pycnidia immersed, globose; ostiole brownish black; conidia filiform, (9.0–)10.0–12.0 μm ~ 1 μm (n = 14).
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 in honor of our colleague and good friend Marcelo Pinto Marcelli, in recognition of his work on the lichen family Parmeliaceae.
Ecology and distribution. Endemic to the Galapagos; apparently rare, few collections from Floreana and Isabela Island (Volcán Darwin and Volcán Sierra Negra); from the dry zone through the transition zone and humid zone into the high altitude dry zone; all specimens from exposed rock surfaces (pebbles, small rocks and boulders).
Notes.Parmotrema marcellianum is overall very similar to P. clavuliferum but is exclusively saxicolous, more conspicuously ciliate, and has much smaller lobes. The species generally lacks an erhizinate zone along its lower lobe margin, and the underside is almost entirely blackened throughout; only rarely is the immediate edge of the lower side of the lobes very dark brown, and sometimes the clavulae have whitish flecks below (unlike those of P. clavuliferum, which are generally white below). The new species is similar in overall appearance to P. herrei (Zahlbr.) Spielmann & Marcelli, but that species presents much longer and branched cilia and it is regularly found with apothecia and lacks vegetative propagules (Marcelli et al. 2011).