limestone fern vs fern

limestone fern and fern both are nouns.

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

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

limestone fern: yellow-green fern of rocky areas of Northern Hemisphere
fern: any of numerous flowerless and seedless vascular plants having true roots from a rhizome and fronds that uncurl upward; reproduce by spores

limestone fern (noun)	fern (noun)
yellow-green fern of rocky areas of Northern Hemisphere	any of numerous flowerless and seedless vascular plants having true roots from a rhizome and fronds that uncurl upward; reproduce by spores