Galapagos Species Database

Thallus thin, often partially embedded in the bark, continuous to rimose, pale creamy white, grayish or ochraceous, ± the same color as the substrate; surface smooth, matt, not pruinose; Apothecia immersed to prominent, lirellate; lirellae broad, short to ±elongate, sparsely branched; labia absent, but with a smooth, prominent thalline margin; disc expanded, flattened, blackened, typically ±covered by an inconspicuous farinose whitish pruina; exciple thin, laterally and basally not carbonized, not expanding, but apically pigmented, ±brownish, not black, typically surrounded by a smooth thalline margin; hymenium hyaline, strongly inspers, I–; ascospores pale gray, soon brown, I+ violet or brownish violet, 1-4 per ascus, broadly oblong, 95-128 x 20-32 µm, densely muriform, 21-31 vs. 4-7 celled. Chemistry: Thallus with norstictic and connorstictic acid, K+ orange-red (crystals).

Because of its broadly expanded, inconspicuously pruinose disc and sparsely branched lirellae P. atromaculata is superficially similar to Sarcographa ramificans. Labia of P. atromaculata are, however, not well developed, instead an often fissured whitish thallus rim typically surrounds the disc. The two species are also clearly distinguished by their secondary chemistry (S. ramificans lacks norstictic acid). Microscopically, P. atromaculata has large, densely muriform ascospores, the exciple is not carbonized and basally poorly developed. Sarcographa ramificans has much smaller, transversely septate spores and a distinctly carbonized exciple that basally expands with age.