Zoysia japonica vs zoysia

Zoysia japonica and zoysia both are nouns.

Word	Noun	Adjective	Verb	Adverb
Zoysia japonica	Yes	No	No	No
zoysia	Yes	No	No	No

As nouns, zoysia is a hypernym of Zoysia japonica; that is, zoysia is a word with a broader meaning than Zoysia japonica:

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

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