Sium sisarum vs marsh plant

Sium sisarum and marsh plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
Sium sisarum	Yes	No	No	No
marsh plant	Yes	No	No	No

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

Sium sisarum: an Asiatic herb cultivated in Europe for its sweet edible tuberous root
marsh plant: a semiaquatic plant that grows in soft wet land; most are monocots: sedge, sphagnum, grasses, cattails, etc; possibly heath

Other hypernyms of Sium sisarum include bog plant, swamp plant.

Sium sisarum (noun)	marsh plant (noun)
an Asiatic herb cultivated in Europe for its sweet edible tuberous root	a semiaquatic plant that grows in soft wet land; most are monocots: sedge, sphagnum, grasses, cattails, etc; possibly heath