marsh plant vs aquatic plant

marsh plant and aquatic plant both are nouns.

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

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

marsh plant: a semiaquatic plant that grows in soft wet land; most are monocots: sedge, sphagnum, grasses, cattails, etc; possibly heath
aquatic plant: a plant that grows partly or wholly in water whether rooted in the mud, as a lotus, or floating without anchorage, as the water hyacinth

Other hypernyms of marsh plant include hydrophyte, hydrophytic plant, water plant.

marsh plant (noun)	aquatic plant (noun)
a semiaquatic plant that grows in soft wet land; most are monocots: sedge, sphagnum, grasses, cattails, etc; possibly heath	a plant that grows partly or wholly in water whether rooted in the mud, as a lotus, or floating without anchorage, as the water hyacinth