bitter orange vs genus Citrus

bitter orange and genus Citrus both are nouns.

Word	Noun	Adjective	Verb	Adverb
bitter orange	Yes	No	No	No
genus Citrus	Yes	No	No	No

bitter orange (noun)	genus Citrus (noun)
highly acidic orange used especially in marmalade	orange, lemon, lime, etc.
any of various common orange trees yielding sour or bitter fruit; used as grafting stock