Salix alba vs willow tree

Salix alba and willow tree both are nouns.

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

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

Salix alba: large willow tree of Eurasia and North Africa having greyish canescent leaves and grey bark
willow tree: any of numerous deciduous trees and shrubs of the genus Salix

Other hypernyms of Salix alba include willow.

Salix alba (noun)	willow tree (noun)
large willow tree of Eurasia and North Africa having greyish canescent leaves and grey bark	any of numerous deciduous trees and shrubs of the genus Salix