lichenism

(li’ken-izm), n. [« lichen + -ism.] The habit of living in that union of fungus and alga which is supposed by many to constitute a lichen. It is moreover quite conceivable that there are species of Algwe which have become so adapted to lichenism that they can no longer attain their full development outside the Lichen-combination. De Bary, Fungi (trans.), p. 419.