common birch vs silver birch

common birch and silver birch both are nouns.

Word	Noun	Adjective	Verb	Adverb
common birch	Yes	No	No	No
silver birch	Yes	No	No	No

As nouns, common birch and silver birch are synonyms defined as:

common birch and silver birch: European birch with silvery white peeling bark and markedly drooping branches

Other synonyms of common birch include Betula pendula, European white birch.

common birch (noun)	silver birch (noun)
European birch with silvery white peeling bark and markedly drooping branches	European birch with silvery white peeling bark and markedly drooping branches