annual fern vs fern

annual fern and fern both are nouns.

Word	Noun	Adjective	Verb	Adverb
annual fern	Yes	No	No	No
fern	Yes	No	No	No

As nouns, fern is a hypernym of annual fern; that is, fern is a word with a broader meaning than annual fern:

annual fern: small short-lived fern of Central and South America
fern: any of numerous flowerless and seedless vascular plants having true roots from a rhizome and fronds that uncurl upward; reproduce by spores

annual fern (noun)	fern (noun)
small short-lived fern of Central and South America	any of numerous flowerless and seedless vascular plants having true roots from a rhizome and fronds that uncurl upward; reproduce by spores