black gum vs black mallee

black gum and black mallee both are nouns.

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

As nouns, black gum and black mallee are synonyms defined as:

black gum and black mallee: a small mallee with rough dark-colored bark toward the butt; yields a red eucalyptus kino gum

Other synonyms of black gum include black sally, Eucalytus stellulata.

black gum (noun)	black mallee (noun)
columnar tree of eastern North America having horizontal limbs and small leaves that emerge late in spring and have brilliant color in early fall	a small mallee with rough dark-colored bark toward the butt; yields a red eucalyptus kino gum
a small mallee with rough dark-colored bark toward the butt; yields a red eucalyptus kino gum