Sium sisarum vs swamp plant

Sium sisarum and swamp plant both are nouns.

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

As nouns, swamp plant is a hypernym of Sium sisarum; that is, swamp 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
swamp 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, marsh plant.

Sium sisarum (noun)	swamp 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