ganja vs Mexican green

ganja and Mexican green both are nouns.

Word	Noun	Adjective	Verb	Adverb
ganja	Yes	No	No	No
Mexican green	Yes	No	No	No

As nouns, Mexican green is a hyponym of ganja; that is, Mexican green is a word with a more specific, narrower meaning than ganja:

ganja: the most commonly used illicit drug; considered a soft drug, it consists of the dried leaves of the hemp plant; smoked or chewed for euphoric effect
Mexican green: a particularly potent variety of marijuana

Other hyponyms of ganja include Acapulco gold, dope, gage, grass, green goddess, locoweed, Mary Jane, pot, sens, sess, skunk, smoke, weed, kief.

ganja (noun)	Mexican green (noun)
the most commonly used illicit drug; considered a soft drug, it consists of the dried leaves of the hemp plant; smoked or chewed for euphoric effect	a particularly potent variety of marijuana
a strong-smelling plant whose dried leaves can be smoked for a pleasant effect or pain reduction