Betula nigra vs black birch

Betula nigra and black birch both are nouns.

Word	Noun	Adjective	Verb	Adverb
Betula nigra	Yes	No	No	No
black birch	Yes	No	No	No

As nouns, Betula nigra and black birch are synonyms defined as:

Betula nigra and black birch: birch of swamps and river bottoms throughout the eastern United States having reddish-brown bark

Other synonyms of Betula nigra include red birch, river birch.

Betula nigra (noun)	black birch (noun)
birch of swamps and river bottoms throughout the eastern United States having reddish-brown bark	birch of swamps and river bottoms throughout the eastern United States having reddish-brown bark
	common birch of the eastern United States having spicy brown bark yielding a volatile oil and hard dark wood used for furniture