mallee vs black mallee

mallee and black mallee both are nouns.

Word	Noun	Adjective	Verb	Adverb
mallee	Yes	No	No	No
black mallee	Yes	No	No	No

As nouns, black mallee is a hyponym of mallee; that is, black mallee is a word with a more specific, narrower meaning than mallee:

mallee: any of several low-growing Australian eucalypts
black mallee: a small mallee with rough dark-colored bark toward the butt; yields a red eucalyptus kino gum

mallee (noun)	black mallee (noun)
any of several low-growing Australian eucalypts	a small mallee with rough dark-colored bark toward the butt; yields a red eucalyptus kino gum