Salix nigra vs willow

Salix nigra and willow both are nouns.

Word	Noun	Adjective	Verb	Adverb
Salix nigra	Yes	No	No	No
willow	Yes	No	No	No

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

Salix nigra: North American shrubby willow having dark bark and linear leaves growing close to streams and lakes
willow: any of numerous deciduous trees and shrubs of the genus Salix

Other hypernyms of Salix nigra include willow tree.

Salix nigra (noun)	willow (noun)
North American shrubby willow having dark bark and linear leaves growing close to streams and lakes	a textile machine having a system of revolving spikes for opening and cleaning raw textile fibers
	any of numerous deciduous trees and shrubs of the genus Salix