Salix sitchensis vs willow tree

Salix sitchensis and willow tree both are nouns.

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

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

Salix sitchensis: small shrubby tree of western North America (Alaska to Oregon)
willow tree: any of numerous deciduous trees and shrubs of the genus Salix

Other hypernyms of Salix sitchensis include willow.

Salix sitchensis (noun)	willow tree (noun)
small shrubby tree of western North America (Alaska to Oregon)	any of numerous deciduous trees and shrubs of the genus Salix