Malus sylvestris vs wild apple

Malus sylvestris and wild apple both are nouns.

Word	Noun	Adjective	Verb	Adverb
Malus sylvestris	Yes	No	No	No
wild apple	Yes	No	No	No

As nouns, wild apple is a hypernym of Malus sylvestris; that is, wild apple is a word with a broader meaning than Malus sylvestris:

Malus sylvestris: wild crab apple native to Europe; a chief ancestor of cultivated apples
wild apple: any of numerous wild apple trees usually with small acidic fruit

Other hypernyms of Malus sylvestris include crab apple, crabapple.

Malus sylvestris (noun)	wild apple (noun)
wild crab apple native to Europe; a chief ancestor of cultivated apples	any of numerous wild apple trees usually with small acidic fruit