red birch vs river birch

red birch and river birch both are nouns.

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

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

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

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

red birch (noun)	river 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