Hydrangea arborescens

Hydrangea arborescens, commonly known as Wild Hydrangea or Smooth Hydrangea, is a species of Hydrangea native to eastern North America.

Cultivation
The cultivar "Annabelle" is the best known of this species. It is one of the most cold hardy of Hydrangeas. The cultivar ‘Grandiflora’ has flowers that resemble snowballs, similar to Viburnum plicatum.