Iceland moss

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A brittle, grayish-brown, Arctic lichen (Cetraria islandica) sometimes used as a food or in medicine.

Century Dictionary and Cyclopedia

1. n. etc. See the nouns.

Wiktionary

1. n. A lichen, Cetraria islandica, that resembles a moss.

GNU Webster's 1913

1. (Bot.) A kind of lichen (Cetraria Icelandica) found from the Arctic regions to the North Temperate zone. It furnishes a nutritious jelly and other forms of food, and is used in pulmonary complaints as a demulcent.
2. n. a lichen. See Iceland Moss.

WordNet 3.0

1. n. lichen with branched flattened partly erect thallus that grows in mountainous and Arctic regions; used as a medicine or food for humans and livestock; a source of glycerol