flax rust fungus vs rust fungus

flax rust fungus and rust fungus both are nouns.

Word	Noun	Adjective	Verb	Adverb
flax rust fungus	Yes	No	No	No
rust fungus	Yes	No	No	No

As nouns, rust fungus is a hypernym of flax rust fungus; that is, rust fungus is a word with a broader meaning than flax rust fungus:

Other hypernyms of flax rust fungus include rust.

flax rust fungus (noun)	rust fungus (noun)
fungus causing flax rust	any of various fungi causing rust disease in plants