Salix repens vs willow tree

Salix repens and willow tree both are nouns.

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

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

Salix repens: small trailing bush of Europe and Asia having straggling branches with silky green leaves of which several varieties are cultivated
willow tree: any of numerous deciduous trees and shrubs of the genus Salix

Other hypernyms of Salix repens include willow.

Salix repens (noun)	willow tree (noun)
small trailing bush of Europe and Asia having straggling branches with silky green leaves of which several varieties are cultivated	any of numerous deciduous trees and shrubs of the genus Salix