Arrhenatherum vs Gramineae

Arrhenatherum and Gramineae both are nouns.

Word	Noun	Adjective	Verb	Adverb
Arrhenatherum	Yes	No	No	No
Gramineae	Yes	No	No	No

Arrhenatherum (noun)	Gramineae (noun)
oat grass	the grasses: chiefly herbaceous but some woody plants including cereals, bamboo, reeds, sugar cane