Quercus variabilis vs oak tree

Quercus variabilis and oak tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
Quercus variabilis	Yes	No	No	No
oak tree	Yes	No	No	No

As nouns, oak tree is a hypernym of Quercus variabilis; that is, oak tree is a word with a broader meaning than Quercus variabilis:

Quercus variabilis: medium to large deciduous tree of China, Japan, and Korea having thick corky bark
oak tree: a deciduous tree of the genus Quercus; has acorns and lobed leaves

Other hypernyms of Quercus variabilis include oak.

Quercus variabilis (noun)	oak tree (noun)
medium to large deciduous tree of China, Japan, and Korea having thick corky bark	a deciduous tree of the genus Quercus; has acorns and lobed leaves