sour gum vs tupelo

sour gum and tupelo both are nouns.

Word	Noun	Adjective	Verb	Adverb
sour gum	Yes	No	No	No
tupelo	Yes	No	No	No

As nouns, tupelo is a hypernym of sour gum; that is, tupelo is a word with a broader meaning than sour gum:

sour gum: columnar tree of eastern North America having horizontal limbs and small leaves that emerge late in spring and have brilliant color in early fall
tupelo: any of several gum trees of swampy areas of North America

Other hypernyms of sour gum include tupelo tree.

sour gum (noun)	tupelo (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	any of several gum trees of swampy areas of North America
	pale soft wood of a tupelo tree especially the water gum