sand myrtle vs shrub

sand myrtle and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
sand myrtle	Yes	No	No	No
shrub	Yes	No	No	No

As nouns, shrub is a hypernym of sand myrtle; that is, shrub is a word with a broader meaning than sand myrtle:

sand myrtle: low-growing evergreen shrub of New Jersey to Florida grown for its many white star-shaped flowers and glossy foliage
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of sand myrtle include bush.

sand myrtle (noun)	shrub (noun)
low-growing evergreen shrub of New Jersey to Florida grown for its many white star-shaped flowers and glossy foliage	a low woody perennial plant usually having several major stems