Word Study
manna lichen
WORDNET DICTIONARY
Noun manna lichen has 1 sense
CIDE DICTIONARY
manna lichen, n.
Any of several Old World semicrustaceous or shrubby lecanoras that roll up and are blown about over African and Arabian deserts and used as food by people and animals; same as manna{2}. [WordNet 1.5]
For further exploring for "manna lichen" in Webster Dictionary Online