Sium sisarum vs bog plant

Sium sisarum and bog plant both are nouns.

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

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

Sium sisarum (noun)	bog 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