Ulmus rubra vs elm tree

Ulmus rubra and elm tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
Ulmus rubra	Yes	No	No	No
elm tree	Yes	No	No	No

As nouns, elm tree is a hypernym of Ulmus rubra; that is, elm tree is a word with a broader meaning than Ulmus rubra:

Ulmus rubra: North American elm having rough leaves that are red when opening; yields a hard wood
elm tree: any of various trees of the genus Ulmus: important timber or shade trees

Other hypernyms of Ulmus rubra include elm.

Ulmus rubra (noun)	elm tree (noun)
North American elm having rough leaves that are red when opening; yields a hard wood	any of various trees of the genus Ulmus: important timber or shade trees