kelpwort vs shrub

kelpwort and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
kelpwort	Yes	No	No	No
shrub	Yes	No	No	No

As nouns, shrub is a hypernym of kelpwort; that is, shrub is a word with a broader meaning than kelpwort:

kelpwort: bushy plant of Old World salt marshes and sea beaches having prickly leaves; burned to produce a crude soda ash
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of kelpwort include bush.

kelpwort (noun)	shrub (noun)
bushy plant of Old World salt marshes and sea beaches having prickly leaves; burned to produce a crude soda ash	a low woody perennial plant usually having several major stems