Agrostis nebulosa vs bent grass

Agrostis nebulosa and bent grass both are nouns.

Word	Noun	Adjective	Verb	Adverb
Agrostis nebulosa	Yes	No	No	No
bent grass	Yes	No	No	No

As nouns, bent grass is a hypernym of Agrostis nebulosa; that is, bent grass is a word with a broader meaning than Agrostis nebulosa:

Agrostis nebulosa: Spanish grass with light feathery panicles grown for dried bouquets
bent grass: grass for pastures and lawns especially bowling and putting greens

Other hypernyms of Agrostis nebulosa include bent-grass, bent.

Agrostis nebulosa (noun)	bent grass (noun)
Spanish grass with light feathery panicles grown for dried bouquets	grass for pastures and lawns especially bowling and putting greens