American dogwood vs dogwood

American dogwood and dogwood both are nouns.

Word	Noun	Adjective	Verb	Adverb
American dogwood	Yes	No	No	No
dogwood	Yes	No	No	No

As nouns, dogwood is a hypernym of American dogwood; that is, dogwood is a word with a broader meaning than American dogwood:

American dogwood: common North American shrub with reddish purple twigs and white flowers
dogwood: a tree of shrub of the genus Cornus often having showy bracts resembling flowers

Other hypernyms of American dogwood include cornel, dogwood tree.

American dogwood (noun)	dogwood (noun)
common North American shrub with reddish purple twigs and white flowers	a tree of shrub of the genus Cornus often having showy bracts resembling flowers
	hard tough wood of any dogwood of the genus Cornus; resembles boxwood