red elm vs September elm

red elm and September elm both are nouns.

Word	Noun	Adjective	Verb	Adverb
red elm	Yes	No	No	No
September elm	Yes	No	No	No

As nouns, red elm and September elm are synonyms defined as:

red elm and September elm: autumn-flowering elm of southeastern United States

Other synonyms of red elm include Ulmus serotina.

red elm (noun)	September elm (noun)
North American elm having rough leaves that are red when opening; yields a hard wood	autumn-flowering elm of southeastern United States
autumn-flowering elm of southeastern United States