Helleborus niger vs black hellebore

Helleborus niger and black hellebore both are nouns.

Word	Noun	Adjective	Verb	Adverb
Helleborus niger	Yes	No	No	No
black hellebore	Yes	No	No	No

As nouns, Helleborus niger and black hellebore are synonyms defined as:

Helleborus niger and black hellebore: European evergreen plant with white or purplish rose-like winter-blooming flowers

Other synonyms of Helleborus niger include Christmas rose, winter rose.

Helleborus niger (noun)	black hellebore (noun)
European evergreen plant with white or purplish rose-like winter-blooming flowers	European evergreen plant with white or purplish rose-like winter-blooming flowers
	slightly hairy perennial having deep green leathery leaves and flowers that are ultimately purplish-green