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