white willow vs Salix alba

white willow and Salix alba both are nouns.

Word	Noun	Adjective	Verb	Adverb
white willow	Yes	No	No	No
Salix alba	Yes	No	No	No

As nouns, white willow and Salix alba are synonyms defined as:

white willow and Salix alba: large willow tree of Eurasia and North Africa having greyish canescent leaves and grey bark

Other synonyms of white willow include Huntingdon willow.

white willow (noun)	Salix alba (noun)
large willow tree of Eurasia and North Africa having greyish canescent leaves and grey bark	large willow tree of Eurasia and North Africa having greyish canescent leaves and grey bark