It is often of a pale chestnut color, but varies considerably, being sometimes almost entirely greyish-white; and grows to a height of from 3 to 4 in., the branches being channelled or rolled into tubes, which end in flattened lobes with fringed edges.
It grows abundantly in the mountainous regions of northern countries, and it is specially characteristic of the lava slopes and plains of the west and north of Iceland. It is found on the mountains of north Wales, northern England, Scotland and south-west Ireland. In North America its range extends through Arctic regions, from Alaska to Newfoundland, and south in the Rocky Mountains to Colorado, and to the Appalachian Mountains of New England.
In commerce it is a light-grey harsh cartilaginous body, almost colorless, and tastes slightly bitter. It contains about 70% of lichenin or lichen-starch, a body isomeric with common starch, but without structure. It also yields a peculiar modification of chlorophyll (called thallochlor), fumaric acid, lichenostearic acid, and cetraric acid (which gives it the bitter taste). It forms a nutritious and easily digested amylaceous food, being used in place of starch in some preparations of cocoa. It also contains lichesterinic acid and protolichesterinic acids.
It is not, however, in great demand, and even in Iceland it is only occasionally used to make folk medicines, and in a few traditional dishes. In earlier times, it was much more widely used in breads, porridges, soups etc. Cetraric acid or cetrarin, a white micro-crystalline powder with a bitter taste, is readily soluble in alcohol, and slightly soluble in water and ether. It has been recommended for medicinal use by alternative medicine sites, in doses of 2 to 4 grains (0.1 to 0.25 grams), as a bitter tonic and aperient. It is traditionally used to relieve chest ailments, irritation of the oral and pharyngeal mucous membranes and to suppress dry cough.
Engraving of Cetraria islandica - Islandslav.jpga from the 18th century botanical work Flora Danica
Cetraria islandica, Zillertaler Alpen, Italy
Cetraria islandica growing in a mat, Uppland, Sweden