mountain ash vs flowering tree

mountain ash and flowering tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
mountain ash	Yes	No	No	No
flowering tree	Yes	No	No	No

As nouns, flowering tree is a hypernym of mountain ash; that is, flowering tree is a word with a broader meaning than mountain ash:

Other hypernyms of mountain ash include angiospermous tree.

mountain ash (noun)	flowering tree (noun)
any of various trees of the genus Sorbus	any tree having seeds and ovules contained in the ovary
low-growing ash of Texas
tree having wood similar to the alpine ash; tallest tree in Australia and tallest hardwood in the world