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 to ±verrucose, not pruinose, corticate; Apothecia prominent to sessile, lirellate; lirellae broad, short to ±elongate, sparsely branched; labia absent, but with a smooth, prominent thalline margin; disc expanded, flattened, with a white, farinose pruina; exciple thin, indistinct, rudimentary, faintly brownish yellow, not carbonized; hymenium hyaline, clear (not inspers), I–; ascospores pale gray, soon brownish, I+ red or reddish brown; 8 per ascus, ellipsoid to narrowly ellipsoid, (16)19-27 x 7-8 µm, transversely septate, (4-)6(-8) celled. Chemistry: Norstictic and connorstictic acid, K+ orange-red (crystals).

All Galapagos specimens are characterized by a rudimentary, barely visible exciple and a well developed thalline margin around relatively broad and short lirellae with an expanded, pruinose grayish-black disc. Superficially similar because of its distinct thalline margin is P. atromaculata, but this species has large, muriform ascospores. Most previous identifications of P. dendritica sensu Weber (1986) belong to P. major; thalli of P. dendritica are generally much better developed, whitish pruinose, corticate with more elongate, narrow, typically branched to stellate lirellae. Staiger (2002) lists P. sericeum var. major among P. intricata, possibly because of the similar thin, embedded thallus, but she mentions that lirellae of P. major are not crowded as it is typical for P. intricans s.str.