flowering crab vs Malus ioensis

flowering crab and Malus ioensis both are nouns.

Word	Noun	Adjective	Verb	Adverb
flowering crab	Yes	No	No	No
Malus ioensis	Yes	No	No	No

As nouns, Malus ioensis is a hypernym of flowering crab; that is, Malus ioensis is a word with a broader meaning than flowering crab:

flowering crab: derived from the Iowa crab and cultivated for its large double pink blossoms
Malus ioensis: wild crab apple of western United States with fragrant pink flowers

Other hypernyms of flowering crab include Iowa crab, Iowa crab apple, prairie crab, western crab apple.

flowering crab (noun)	Malus ioensis (noun)
small tree or shrub of southeastern United States; cultivated as an ornamental for its rose-colored blossoms	wild crab apple of western United States with fragrant pink flowers
derived from the Iowa crab and cultivated for its large double pink blossoms