About Umbilicaria hyperborea (Ach.) Hoffm.
The thallus of Umbilicaria hyperborea ranges in colour from medium to dark brown. The upper surface of the thallus has a texture that is more or less smooth or warty. The undersurface of the thallus is smooth, and it does not produce any rhizines. Its apothecia are disc-shaped, range from flat to convex in shape, and feature multiple complex ridges. This lichen typically grows on rock in arctic and alpine climates. It has also been recorded growing on acidic wood; specimens found on this substrate may have a changed morphology compared to those growing on rock, including stunted, faded thalli that do not have apothecia. It is one of the most common species of Umbilicaria in the Arctic and adjacent northern locations. Umbilicaria hyperborea has a very slow growth rate. A study conducted in Greenland between 1933 and 1970 measured its growth as 0.3 to 0.4 mm per year.
