Pertusaria pseudocorallina (Lilj.) Arnold forme maritime
This form, which deserves a particular study, differs from the type by the presence of very large club-shaped isidia, brown, darker at the top, (up to 2.5-3 mm in height) clustered in large heaps on the thallus. It is also characterized by a more or less zoned, blackish prothallus and color reactions slightly different color reactions of the type: C-, KC+ pale yellow, K+ yellow with a little reddish brown, P+ orange. This form occurs on the very exposed, slightly acid rocks of the Caps et Pointes in the far west of Finistère.
N.B. Pertusaria coccodes that seldom grows on rocks has similar chemical spot tests (although KC+ yellow), but its isidia, also potentially heaps forming, are grey, smaller, its thallus is more greyish devoid of pink.