Prunus salicina vs plum tree

Prunus salicina and plum tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
Prunus salicina	Yes	No	No	No
plum tree	Yes	No	No	No

As nouns, plum tree is a hypernym of Prunus salicina; that is, plum tree is a word with a broader meaning than Prunus salicina:

Prunus salicina: small tree of China and Japan bearing large yellow to red plums usually somewhat inferior to European plums in flavor
plum tree: any of several trees producing edible oval fruit having a smooth skin and a single hard stone

Other hypernyms of Prunus salicina include plum.

Prunus salicina (noun)	plum tree (noun)
small tree of China and Japan bearing large yellow to red plums usually somewhat inferior to European plums in flavor	any of several trees producing edible oval fruit having a smooth skin and a single hard stone