genus Salix vs willow tree

genus Salix and willow tree both are nouns.

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

genus Salix (noun)	willow tree (noun)
a large and widespread genus varying in size from small shrubs to large trees: willows	any of numerous deciduous trees and shrubs of the genus Salix