white alder vs mountain alder

white alder and mountain alder both are nouns.

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

As nouns, white alder and mountain alder are synonyms defined as:

Other synonyms of white alder include Alnus rhombifolia.

white alder (noun)	mountain alder (noun)
tree of western United States	small shrubby maple of eastern North America; scarlet in autumn
shrub of eastern and southern coastal United States having beautiful racemes of spice-scented white flowers	tree of western United States