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