Knowlton's cactus vs cactus

Knowlton's cactus and cactus both are nouns.

Word	Noun	Adjective	Verb	Adverb
Knowlton's cactus	Yes	No	No	No
cactus	Yes	No	No	No

As nouns, cactus is a hypernym of Knowlton's cactus; that is, cactus is a word with a broader meaning than Knowlton's cactus:

Knowlton's cactus: small clustering cactus of southwestern United States; a threatened species
cactus: any succulent plant of the family Cactaceae native chiefly to arid regions of the New World and usually having spines

Knowlton's cactus (noun)	cactus (noun)
small clustering cactus of southwestern United States; a threatened species	any succulent plant of the family Cactaceae native chiefly to arid regions of the New World and usually having spines