Ulmus americana vs American elm

Ulmus americana and American elm both are nouns.

Word	Noun	Adjective	Verb	Adverb
Ulmus americana	Yes	No	No	No
American elm	Yes	No	No	No

As nouns, Ulmus americana and American elm are synonyms defined as:

Ulmus americana and American elm: large ornamental tree with graceful gradually spreading branches common in eastern North America

Other synonyms of Ulmus americana include rock elm, water elm, white elm.

Ulmus americana (noun)	American elm (noun)
large ornamental tree with graceful gradually spreading branches common in eastern North America	large ornamental tree with graceful gradually spreading branches common in eastern North America