Oryzopsis miliacea vs ricegrass

Oryzopsis miliacea and ricegrass both are nouns.

Word	Noun	Adjective	Verb	Adverb
Oryzopsis miliacea	Yes	No	No	No
ricegrass	Yes	No	No	No

As nouns, ricegrass is a hypernym of Oryzopsis miliacea; that is, ricegrass is a word with a broader meaning than Oryzopsis miliacea:

Oryzopsis miliacea: perennial mountain rice native to Mediterranean region and introduced into North America
ricegrass: any grass of the genus Oryzopsis

Other hypernyms of Oryzopsis miliacea include rice grass.

Oryzopsis miliacea (noun)	ricegrass (noun)
perennial mountain rice native to Mediterranean region and introduced into North America	any grass of the genus Oryzopsis