Sorbus sitchensis vs Western mountain ash

Sorbus sitchensis and Western mountain ash both are nouns.

Word	Noun	Adjective	Verb	Adverb
Sorbus sitchensis	Yes	No	No	No
Western mountain ash	Yes	No	No	No

As nouns, Sorbus sitchensis and Western mountain ash are synonyms defined as:

Sorbus sitchensis and Western mountain ash: an ash of the western coast of North America

Sorbus sitchensis (noun)	Western mountain ash (noun)
an ash of the western coast of North America	an ash of the western coast of North America