Iceland moss (Cetraria islandica) is a lichen whose erect or ascending foliaceous habit gives it something of the appearance of a moss, whence probably the name. 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 terminate 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, north 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.
As met with in commerce it is a light-grey harsh cartilaginous body, almost destitute of color, and having a slightly bitter taste. It contains about 70% of lichenin or lichen-starch, a body isomeric with common starch, but wanting any appearance of structure. It also yields a peculiar modification of chlorophyll (called thallochlor), fumaric acid, lichenostearic acid, and cetraric acid (to which last it owes its 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, 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.
Engraving of Cetraria islandica - Islandslav.jpga from the 18th century botanical work Flora Danica
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