white alder vs shrub

white alder and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
white alder	Yes	No	No	No
shrub	Yes	No	No	No

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

white alder: shrub of eastern and southern coastal United States having beautiful racemes of spice-scented white flowers
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of white alder include bush.

white alder (noun)	shrub (noun)
tree of western United States	a low woody perennial plant usually having several major stems
shrub of eastern and southern coastal United States having beautiful racemes of spice-scented white flowers