swamp willow vs Salix nigra

swamp willow and Salix nigra both are nouns.

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

As nouns, swamp willow and Salix nigra are synonyms defined as:

swamp willow and Salix nigra: North American shrubby willow having dark bark and linear leaves growing close to streams and lakes

Other synonyms of swamp willow include black willow.

swamp willow (noun)	Salix nigra (noun)
North American shrubby willow having dark bark and linear leaves growing close to streams and lakes	North American shrubby willow having dark bark and linear leaves growing close to streams and lakes