water parsnip vs bog plant

water parsnip and bog plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
water parsnip	Yes	No	No	No
bog plant	Yes	No	No	No

As nouns, bog plant is a hypernym of water parsnip; that is, bog plant is a word with a broader meaning than water parsnip:

water parsnip: stout white-flowered perennial found wild in shallow fresh water; northern United States and Asia
bog plant: a semiaquatic plant that grows in soft wet land; most are monocots: sedge, sphagnum, grasses, cattails, etc; possibly heath

Other hypernyms of water parsnip include marsh plant, swamp plant.

water parsnip (noun)	bog plant (noun)
stout white-flowered perennial found wild in shallow fresh water; northern United States and Asia	a semiaquatic plant that grows in soft wet land; most are monocots: sedge, sphagnum, grasses, cattails, etc; possibly heath