white elm vs Ulmus americana

white elm and Ulmus americana both are nouns.

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

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

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

Other synonyms of white elm include American elm, rock elm, water elm.

white elm (noun)	Ulmus americana (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