roccella vs lichen

roccella and lichen both are nouns.

Word	Noun	Adjective	Verb	Adverb
roccella	Yes	No	No	No
lichen	Yes	No	No	No

As nouns, lichen is a hypernym of roccella; that is, lichen is a word with a broader meaning than roccella:

roccella: a source of the dye archil and of litmus
lichen: any thallophytic plant of the division Lichenes; occur as crusty patches or bushy growths on tree trunks or rocks or bare ground etc.

roccella (noun)	lichen (noun)
a source of the dye archil and of litmus	any thallophytic plant of the division Lichenes; occur as crusty patches or bushy growths on tree trunks or rocks or bare ground etc.
	any of several eruptive skin diseases characterized by hard thick lesions grouped together and resembling lichens growing on rocks