Galapagos Species Database

Thallus thin, continuous to rimose, white to creamy white; surface dull, whitish pruinose, corticate; Apothecia immersed to erumpent (three specimens in CDS have a very poorly developed thallus where the apothecia appear prominent), lirellate; lirellae slender, elongate, sparsely to moderately branched; labia thin, entire (attention: because of thalline margin appearing striate), black, typically densely whitish pruinose, hemmed in by a thin thallus rim, which is distinctly separated from the thallus by a thin fissure; disc ±open, grayish white pruinose where visible; exciple laterally carbonized, open below; hymenium hyaline, clear (not inspers); ascospores hyaline, I+ bluish violet, 8 per ascus, fusiform, 20-41 x 6-8 µm, transversely septate, 6-10 celled. Chemistry: Norstictic acid, K+ orange-red (forming needle shaped crystals).

One specimen at CDS (Aptroot 63779) has submuriform spores (i.e., with a few longitudinal septa), but otherwise agrees well with G. caesiella. Species with thin, moderately branched lirellae and a white thallus are all quite similar, but G. caesiella is the only species with white pruinose lirellae and a thallus reacting K+ orange (red crystals). Graphis crebra, a species that also reacts K+ orange (red crystals), typically has shorter unbranched lirellae, a much wider, distinctly open, pruinose disc, labia which are strongly blackened and not pruinose, and an inspers hymenium. Other superficially similar species are G. tenella, G. intricata and G. elongata (for discussion see especially G. elongata).