river birch vs red birch

river birch and red birch both are nouns.

Word	Noun	Adjective	Verb	Adverb
river birch	Yes	No	No	No
red birch	Yes	No	No	No

As nouns, river birch and red birch are synonyms defined as:

river birch and red birch: birch of swamps and river bottoms throughout the eastern United States having reddish-brown bark

Other synonyms of river birch include Betula nigra, black birch.

river birch (noun)	red birch (noun)
birch of swamps and river bottoms throughout the eastern United States having reddish-brown bark	birch of swamps and river bottoms throughout the eastern United States having reddish-brown bark