indigo broom vs wild indigo

indigo broom and wild indigo both are nouns.

Word	Noun	Adjective	Verb	Adverb
indigo broom	Yes	No	No	No
wild indigo	Yes	No	No	No

As nouns, wild indigo is a hypernym of indigo broom; that is, wild indigo is a word with a broader meaning than indigo broom:

indigo broom: much-branched erect herb with bright yellow flowers; distributed from Massachusetts to Florida
wild indigo: any of several plants of the genus Baptisia

Other hypernyms of indigo broom include false indigo.

indigo broom (noun)	wild indigo (noun)
much-branched erect herb with bright yellow flowers; distributed from Massachusetts to Florida	any of several plants of the genus Baptisia