wild indigo vs ligneous plant

wild indigo and ligneous plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
wild indigo	Yes	No	No	No
ligneous plant	Yes	No	No	No

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

wild indigo: any of several plants of the genus Baptisia
ligneous plant: a plant having hard lignified tissues or woody parts especially stems

Other hypernyms of wild indigo include woody plant.

wild indigo (noun)	ligneous plant (noun)
any of several plants of the genus Baptisia	a plant having hard lignified tissues or woody parts especially stems