Caltha palustris vs marsh plant

Caltha palustris and marsh plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
Caltha palustris	Yes	No	No	No
marsh plant	Yes	No	No	No

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

Caltha palustris: 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 Caltha palustris include bog plant, swamp plant.

Caltha palustris (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