hardheads vs lesser knapweed

hardheads and lesser knapweed both are nouns.

Word	Noun	Adjective	Verb	Adverb
hardheads	Yes	No	No	No
lesser knapweed	Yes	No	No	No

As nouns, hardheads and lesser knapweed are synonyms defined as:

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

Other synonyms of hardheads include black knapweed, Centaurea nigra.

hardheads (noun)	lesser knapweed (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