dogwood vs red osier

dogwood and red osier both are nouns.

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

As nouns, red osier is a hyponym of dogwood; that is, red osier 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 osier: common North American shrub with reddish purple twigs and white flowers

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