grass-of-Parnassus vs parnassia

grass-of-Parnassus and parnassia both are nouns.

Word	Noun	Adjective	Verb	Adverb
grass-of-Parnassus	Yes	No	No	No
parnassia	Yes	No	No	No

As nouns, grass-of-Parnassus and parnassia are synonyms defined as:

grass-of-Parnassus and parnassia: any of various usually evergreen bog plants of the genus Parnassia having broad smooth basal leaves and a single pale flower resembling a buttercup

grass-of-Parnassus (noun)	parnassia (noun)
any of various usually evergreen bog plants of the genus Parnassia having broad smooth basal leaves and a single pale flower resembling a buttercup	any of various usually evergreen bog plants of the genus Parnassia having broad smooth basal leaves and a single pale flower resembling a buttercup