American gray birch vs genus Betula

American gray birch and genus Betula both are nouns.

Word	Noun	Adjective	Verb	Adverb
American gray birch	Yes	No	No	No
genus Betula	Yes	No	No	No

American gray birch (noun)	genus Betula (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	a genus of trees of the family Betulaceae (such as birches)