ribbon fern vs adder's tongue

ribbon fern and adder's tongue both are nouns.

Word	Noun	Adjective	Verb	Adverb
ribbon fern	Yes	No	No	No
adder's tongue	Yes	No	No	No

As nouns, adder's tongue is a hypernym of ribbon fern; that is, adder's tongue is a word with a broader meaning than ribbon fern:

ribbon fern: epiphytic fern with straplike usually twisted fronds of tropical Asia and Polynesia and America
adder's tongue: ferns with fertile spikes shaped like a snake's tongue

Other hypernyms of ribbon fern include adder's tongue fern.

ribbon fern (noun)	adder's tongue (noun)
fern of North Africa and Azores and Canary Islands	ferns with fertile spikes shaped like a snake's tongue
epiphytic fern with straplike usually twisted fronds of tropical Asia and Polynesia and America
epiphytic fern found in lowland forests of tropical America