Japanese lawn grass vs zoysia

Japanese lawn grass and zoysia both are nouns.

Word	Noun	Adjective	Verb	Adverb
Japanese lawn grass	Yes	No	No	No
zoysia	Yes	No	No	No

As nouns, zoysia is a hypernym of Japanese lawn grass; that is, zoysia is a word with a broader meaning than Japanese lawn grass:

Japanese lawn grass: lawn grass common in China and Japan; grown also in United States
zoysia: any of several creeping grasses of the genus Zoysia

Japanese lawn grass (noun)	zoysia (noun)
lawn grass common in China and Japan; grown also in United States	any of several creeping grasses of the genus Zoysia