Rumex acetosella vs sour grass

Rumex acetosella and sour grass both are nouns.

Word	Noun	Adjective	Verb	Adverb
Rumex acetosella	Yes	No	No	No
sour grass	Yes	No	No	No

As nouns, sour grass is a hypernym of Rumex acetosella; that is, sour grass is a word with a broader meaning than Rumex acetosella:

Rumex acetosella: small plant having pleasantly acid-tasting arrow-shaped leaves; common in dry places
sour grass: any of certain coarse weedy plants with long taproots, sometimes used as table greens or in folk medicine

Other hypernyms of Rumex acetosella include dock, sorrel.

Rumex acetosella (noun)	sour grass (noun)
small plant having pleasantly acid-tasting arrow-shaped leaves; common in dry places	any of certain coarse weedy plants with long taproots, sometimes used as table greens or in folk medicine