noun
or reindeer lichen
: any fruticose lichen of the genus Cladonia ; especially : a gray erect tufted and much-branched lichen ( C. rangiferina ) that is found in extensive patches on the ground in arctic and even in north temperate regions and forms a large part of the food of reindeer and caribou in the far north (as in Lapland) and is sometimes eaten by man — called also arctic moss