flooded gum vs eucalyptus tree

flooded gum and eucalyptus tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
flooded gum	Yes	No	No	No
eucalyptus tree	Yes	No	No	No

As nouns, eucalyptus tree is a hypernym of flooded gum; that is, eucalyptus tree is a word with a broader meaning than flooded gum:

flooded gum: any of several Australian gum trees growing on moist or alluvial soil
eucalyptus tree: a tree of the genus Eucalyptus

Other hypernyms of flooded gum include eucalypt, eucalyptus.

flooded gum (noun)	eucalyptus tree (noun)
any of several Australian gum trees growing on moist or alluvial soil	a tree of the genus Eucalyptus