American grey birch vs gray birch

American grey birch and gray birch both are nouns.

Word	Noun	Adjective	Verb	Adverb
American grey birch	Yes	No	No	No
gray birch	Yes	No	No	No

As nouns, American grey birch and gray birch are synonyms defined as:

American grey birch and gray birch: medium-sized birch of eastern North America having white or pale grey bark and valueless wood; occurs often as a second-growth forest tree

Other synonyms of American grey birch include American gray birch, Betula populifolia, grey birch.

American grey birch (noun)	gray birch (noun)
medium-sized birch of eastern North America having white or pale grey bark and valueless wood; occurs often as a second-growth forest tree	medium-sized birch of eastern North America having white or pale grey bark and valueless wood; occurs often as a second-growth forest tree