Lathagrium cristatum (L.) Otalora, M. M. Jorg & Wedin var. cristatum
Collema cristatum (L.) Weber ex F. H. Wigg.
Tallus foliose, forming dense tufts rosette-shaped, 2-6 cm diam., deeply lobed, lobes wrinkled, notably concave as minute canals, rather thin, narrow, 2-3 mm wide, radiating up to 1 cm long, margin sometimes highly incised, upper surface olive-green when humid, green-brown to green-black when dry, smooth but sometimes with warted or globular isidia towards the center (if they are very abundant: var. marginale), lower surface with pale rhizines. Apothecia more or less abundant, sessile, 2-5 mm diam., disc concave, then flat to slightly convex, red to brown-red, even thalline margin, thin , smooth or granular. Ascospores ellipsoid, with ± acute ends, submuriform (3-septate possibly subdividing), 18-30 x 8-12 µm. Photobiont : Nostoc. Chemical spot tests negative. Usually firmly attached to calcareous rocks and mortar of walls. In our prospection area, this species has also been found on calcareous dunes.*