Cornus, commonly known as dogwood, is a genus of about 30–60 species of woody plants in the family Cornaceae.
Dogwood represents a four-petaled flower with a characteristic center, but just like the poinsettia, the four petals are bracts (specialized leaves) that surround the actual inconspicuous flowers in the center.
Two of the most commonly depicted species are Cornus florida (hanamizuki) and Cornus kousa (yamaboushi). The former has rounded, notched bract "petals" while the latter has pointed ones.
This tag implicates flower (learn more).