Salix pentandra vs willow tree

Salix pentandra and willow tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
Salix pentandra	Yes	No	No	No
willow tree	Yes	No	No	No

As nouns, willow tree is a hypernym of Salix pentandra; that is, willow tree is a word with a broader meaning than Salix pentandra:

Salix pentandra: European willow tree with shining leathery leaves; widely naturalized in the eastern United States
willow tree: any of numerous deciduous trees and shrubs of the genus Salix

Other hypernyms of Salix pentandra include willow.

Salix pentandra (noun)	willow tree (noun)
European willow tree with shining leathery leaves; widely naturalized in the eastern United States	any of numerous deciduous trees and shrubs of the genus Salix