fern ally vs club-moss

fern ally and club-moss both are nouns.

Word	Noun	Adjective	Verb	Adverb
fern ally	Yes	No	No	No
club-moss	Yes	No	No	No

As nouns, club-moss is a hyponym of fern ally; that is, club-moss is a word with a more specific, narrower meaning than fern ally:

fern ally: pteridophytes of other classes than Filicopsida
club-moss: primitive evergreen moss-like plant with spores in club-shaped strobiles

Other hyponyms of fern ally include whisk fern, horsetail, club moss, lycopod, quillwort.

fern ally (noun)	club-moss (noun)
pteridophytes of other classes than Filicopsida	primitive evergreen moss-like plant with spores in club-shaped strobiles