downy birch vs white birch

downy birch and white birch both are nouns.

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

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

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

Other synonyms of downy birch include Betula pubescens.

downy birch (noun)	white 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