mountain birch vs water birch

mountain birch and water birch both are nouns.

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

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

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

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

mountain birch (noun)	water 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