bog hemp vs China grass

bog hemp and China grass both are nouns.

Word	Noun	Adjective	Verb	Adverb
bog hemp	Yes	No	No	No
China grass	Yes	No	No	No

As nouns, China grass is a hyponym of bog hemp; that is, China grass is a word with a more specific, narrower meaning than bog hemp:

bog hemp: any of several flowering weeds of the genus Boehmeria lacking stinging hairs
China grass: tall perennial herb of tropical Asia with dark green leaves; cultivated for the fiber from its woody stems that resembles flax

Other hyponyms of bog hemp include Boehmeria nivea, Chinese silk plant, ramee, ramie.

bog hemp (noun)	China grass (noun)
any of several flowering weeds of the genus Boehmeria lacking stinging hairs	tall perennial herb of tropical Asia with dark green leaves; cultivated for the fiber from its woody stems that resembles flax