Christmas green vs club-moss

Christmas green and club-moss both are nouns.

Word	Noun	Adjective	Verb	Adverb
Christmas green	Yes	No	No	No
club-moss	Yes	No	No	No

As nouns, club-moss is a hypernym of Christmas green; that is, club-moss is a word with a broader meaning than Christmas green:

Christmas green: any of several club mosses having long creeping stems and erect branches
club-moss: primitive evergreen moss-like plant with spores in club-shaped strobiles

Other hypernyms of Christmas green include club moss, lycopod.

Christmas green (noun)	club-moss (noun)
any of several club mosses having long creeping stems and erect branches	primitive evergreen moss-like plant with spores in club-shaped strobiles