American centaury vs sabbatia

American centaury and sabbatia both are nouns.

Word	Noun	Adjective	Verb	Adverb
American centaury	Yes	No	No	No
sabbatia	Yes	No	No	No

As nouns, sabbatia is a hypernym of American centaury; that is, sabbatia is a word with a broader meaning than American centaury:

American centaury: any of several pink-flowered marsh plant of the eastern United States resembling a true centaury
sabbatia: any of various plants of the genus Sabbatia having usually pink cymose flowers; occur from acid bogs to brackish marshes

American centaury (noun)	sabbatia (noun)
any of several pink-flowered marsh plant of the eastern United States resembling a true centaury	any of various plants of the genus Sabbatia having usually pink cymose flowers; occur from acid bogs to brackish marshes