Fraxinus excelsior vs ash tree

Fraxinus excelsior and ash tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
Fraxinus excelsior	Yes	No	No	No
ash tree	Yes	No	No	No

As nouns, ash tree is a hypernym of Fraxinus excelsior; that is, ash tree is a word with a broader meaning than Fraxinus excelsior:

Fraxinus excelsior: tall ash of Europe to the Caucasus having leaves shiny dark-green above and pale downy beneath
ash tree: any of various deciduous pinnate-leaved ornamental or timber trees of the genus Fraxinus

Other hypernyms of Fraxinus excelsior include ash.

Fraxinus excelsior (noun)	ash tree (noun)
tall ash of Europe to the Caucasus having leaves shiny dark-green above and pale downy beneath	any of various deciduous pinnate-leaved ornamental or timber trees of the genus Fraxinus