flowering crab vs prairie crab

flowering crab and prairie crab both are nouns.

Word	Noun	Adjective	Verb	Adverb
flowering crab	Yes	No	No	No
prairie crab	Yes	No	No	No

As nouns, prairie crab is a hypernym of flowering crab; that is, prairie crab 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
prairie crab: wild crab apple of western United States with fragrant pink flowers

Other hypernyms of flowering crab include Iowa crab, Iowa crab apple, Malus ioensis, western crab apple.

flowering crab (noun)	prairie crab (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