Buttonbush (Cephalanthus occidentalis) Zones 4-9
Height: 5-12'
Spread: 4-8'
Growth rate: medium
Wet to moist soils. Sun or partial shade. Yellow fall color. Produces white, button-shaped flowers in late summer and bears seed beneficial to wildlife. Flowers are a great nectar source for butterflies. 
 
Photo credit: Iowa Department of Natural Resources