river gum vs river red gum

river gum and river red gum both are nouns.

Word	Noun	Adjective	Verb	Adverb
river gum	Yes	No	No	No
river red gum	Yes	No	No	No

As nouns, river gum and river red gum are synonyms defined as:

river gum and river red gum: somewhat crooked red gum tree growing chiefly along rivers; has durable reddish lumber used in heavy construction

Other synonyms of river gum include Eucalyptus camaldulensis, Eucalyptus rostrata.

river gum (noun)	river red gum (noun)
somewhat crooked red gum tree growing chiefly along rivers; has durable reddish lumber used in heavy construction	somewhat crooked red gum tree growing chiefly along rivers; has durable reddish lumber used in heavy construction