Citrus nobilis vs orange tree

Citrus nobilis and orange tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
Citrus nobilis	Yes	No	No	No
orange tree	Yes	No	No	No

As nouns, orange tree is a hypernym of Citrus nobilis; that is, orange tree is a word with a broader meaning than Citrus nobilis:

Citrus nobilis: large citrus tree having large sweet deep orange fruit that is easily peeled; widely cultivated in Florida
orange tree: any citrus tree bearing oranges

Other hypernyms of Citrus nobilis include orange.

Citrus nobilis (noun)	orange tree (noun)
large citrus tree having large sweet deep orange fruit that is easily peeled; widely cultivated in Florida	any citrus tree bearing oranges