mountain azalea vs shrub

mountain azalea and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
mountain azalea	Yes	No	No	No
shrub	Yes	No	No	No

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

mountain azalea: creeping mat-forming evergreen shrub of high mountain regions of Northern Hemisphere grown for its rose-pink flowers
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of mountain azalea include bush.

mountain azalea (noun)	shrub (noun)
creeping mat-forming evergreen shrub of high mountain regions of Northern Hemisphere grown for its rose-pink flowers	a low woody perennial plant usually having several major stems