dogwood vs red dogwood

dogwood and red dogwood both are nouns.

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

As nouns, red dogwood is a hyponym of dogwood; that is, red dogwood is a word with a more specific, narrower meaning than dogwood:

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

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