Though the fall-flowering branch of Cornus (Dogwood) might be a somatic
mutant ("sport"), it is also possible that the branch is being affected
by a nearby light source, such as a campus lamp along the promenade.
Is the branch indeed under a lamp post, or other strong nocturnal light
source? Alternatively, are some of the roots near an underground steam
pipe? This is the time of year when campuses turn on the heat, and underground
pipes could be warming a portion of your dogwood's root system, the portion
linked to that particular branch.
Medford, MA 02155