indigo plant vs shrub

indigo plant and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
indigo plant	Yes	No	No	No
shrub	Yes	No	No	No

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

indigo plant: deciduous subshrub of southeastern Asia having pinnate leaves and clusters of red or purple flowers; a source of indigo dye
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of indigo plant include bush.

indigo plant (noun)	shrub (noun)
deciduous subshrub of southeastern Asia having pinnate leaves and clusters of red or purple flowers; a source of indigo dye	a low woody perennial plant usually having several major stems