water plantain vs marsh plant

water plantain and marsh plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
water plantain	Yes	No	No	No
marsh plant	Yes	No	No	No

As nouns, marsh plant is a hypernym of water plantain; that is, marsh plant is a word with a broader meaning than water plantain:

water plantain: marsh plant having clusters of small white or pinkish flowers and broad pointed or rounded leaves
marsh plant: a semiaquatic plant that grows in soft wet land; most are monocots: sedge, sphagnum, grasses, cattails, etc; possibly heath

Other hypernyms of water plantain include bog plant, swamp plant.

water plantain (noun)	marsh plant (noun)
marsh plant having clusters of small white or pinkish flowers and broad pointed or rounded leaves	a semiaquatic plant that grows in soft wet land; most are monocots: sedge, sphagnum, grasses, cattails, etc; possibly heath