swamp lily vs swamp plant

swamp lily and swamp plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
swamp lily	Yes	No	No	No
swamp plant	Yes	No	No	No

As nouns, swamp plant is a hypernym of swamp lily; that is, swamp plant is a word with a broader meaning than swamp lily:

swamp lily: North American herbaceous perennial of wet places having slender curled racemes of small white flowers
swamp plant: a semiaquatic plant that grows in soft wet land; most are monocots: sedge, sphagnum, grasses, cattails, etc; possibly heath

Other hypernyms of swamp lily include bog plant, marsh plant.

swamp lily (noun)	swamp plant (noun)
North American herbaceous perennial of wet places having slender curled racemes of small white flowers	a semiaquatic plant that grows in soft wet land; most are monocots: sedge, sphagnum, grasses, cattails, etc; possibly heath