white birch vs downy birch

white birch and downy birch both are nouns.

Word	Noun	Adjective	Verb	Adverb
white birch	Yes	No	No	No
downy birch	Yes	No	No	No

As nouns, white birch and downy birch are synonyms defined as:

white birch and downy birch: European birch with dull white to pale brown bark and somewhat drooping hairy branches

Other synonyms of white birch include Betula pubescens.

white birch (noun)	downy birch (noun)
European birch with dull white to pale brown bark and somewhat drooping hairy branches	European birch with dull white to pale brown bark and somewhat drooping hairy branches