Collemopsidium halodytes (Nyl.) Grube & B. D. Ryan
Pyrenocollema halodytes (Nyl.) Grube & B. D. Ryan
Thallus superficial, translucent at first, then opaque, pale brown, brownish, smooth, more or less regular, without black ridges, sometimes with minute black or brown dots. Perithecia flattened, sessile, 0.1-0.4 mm, involucrellum spreading laterally, in old specimen ostiole deeply immersed lifebelt-like. Ascospores oblong, 1-septate, 13-22 x 5-9 µm. Pycnidia common, resembling to perithecia but smaller. Photobiont : cyanobacteria. On siliceous or calcareous rocks or boulders in the littoral zone (see also Collemopsidium halodytes forme sur Patella with a thallus and rather similar). This species can be distinguished from Collemopsidium elegans by the absence of warts and ridges on the thallus and its flattened perithecia. Verrucaria ditmarsica s.l. may also be confused but its perithecia are hemispherical, ascospores simple and it grows higher on the foreshore.
This species is considered here stricto sensu.