Gramineae vs Arrhenatherum

Gramineae and Arrhenatherum both are nouns.

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

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