marsh marigold vs marsh plant

marsh marigold and marsh plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
marsh marigold	Yes	No	No	No
marsh plant	Yes	No	No	No

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

marsh marigold: swamp plant of Europe and North America having bright yellow flowers resembling buttercups
marsh plant: a semiaquatic plant that grows in soft wet land; most are monocots: sedge, sphagnum, grasses, cattails, etc; possibly heath

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

marsh marigold (noun)	marsh plant (noun)
swamp plant of Europe and North America having bright yellow flowers resembling buttercups	a semiaquatic plant that grows in soft wet land; most are monocots: sedge, sphagnum, grasses, cattails, etc; possibly heath