Salix sericea vs willow tree

Salix sericea and willow tree both are nouns.

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

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

Salix sericea: North American willow with greyish silky pubescent leaves that usually blacken in drying
willow tree: any of numerous deciduous trees and shrubs of the genus Salix

Other hypernyms of Salix sericea include willow.

Salix sericea (noun)	willow tree (noun)
North American willow with greyish silky pubescent leaves that usually blacken in drying	any of numerous deciduous trees and shrubs of the genus Salix