Apocynum x floribundum Greene (pro sp.)
Family: Apocynaceae
hybrid dogbane, intermediate dogbane
[Apocynum jonesii Woodson,  more...]
Apocynum x floribundum image
from USDA Plants website  
Etymology: Apocynum: from the Greek for "away from dog," i.e. noxious to dogs, in reference to its ancient use as a dog poison, hence dogbane
Plants: erect, perennial forb
Conservation Status: Native