manna grass vs meadowgrass

manna grass and meadowgrass both are nouns.

Word	Noun	Adjective	Verb	Adverb
manna grass	Yes	No	No	No
meadowgrass	Yes	No	No	No

As nouns, meadowgrass is a hypernym of manna grass; that is, meadowgrass is a word with a broader meaning than manna grass:

manna grass: any of several moisture-loving grasses of the genus Glyceria having sweet flavor or odor
meadowgrass: any of various grasses that thrive in the presence of abundant moisture

Other hypernyms of manna grass include meadow grass.

manna grass (noun)	meadowgrass (noun)
any of several moisture-loving grasses of the genus Glyceria having sweet flavor or odor	any of various grasses that thrive in the presence of abundant moisture