lesser knapweed vs Centaurea nigra

lesser knapweed and Centaurea nigra both are nouns.

Word	Noun	Adjective	Verb	Adverb
lesser knapweed	Yes	No	No	No
Centaurea nigra	Yes	No	No	No

As nouns, lesser knapweed and Centaurea nigra are synonyms defined as:

lesser knapweed and Centaurea nigra: a weedy perennial with tough wiry stems and purple flowers; native to Europe but widely naturalized

Other synonyms of lesser knapweed include black knapweed, hardheads.

lesser knapweed (noun)	Centaurea nigra (noun)
a weedy perennial with tough wiry stems and purple flowers; native to Europe but widely naturalized	a weedy perennial with tough wiry stems and purple flowers; native to Europe but widely naturalized