genus Betula vs gray birch

genus Betula and gray birch both are nouns.

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

genus Betula (noun)	gray birch (noun)
a genus of trees of the family Betulaceae (such as birches)	medium-sized birch of eastern North America having white or pale grey bark and valueless wood; occurs often as a second-growth forest tree