water birch vs mountain birch

water birch and mountain birch both are nouns.

Word	Noun	Adjective	Verb	Adverb
water birch	Yes	No	No	No
mountain birch	Yes	No	No	No

As nouns, water birch and mountain birch are synonyms defined as:

water birch and mountain birch: birch of western United States resembling the paper birch but having brownish bark

Other synonyms of water birch include Betula fontinalis, swamp birch, Western birch, Western paper birch.

water birch (noun)	mountain birch (noun)
birch of western United States resembling the paper birch but having brownish bark	birch of western United States resembling the paper birch but having brownish bark