Printed at http://plantfinder.nativeplanttrust.org/index.cfm/
Hydrangea arborescens
smooth hydrangea, American hydrangea
Most common garden Hydrangea sport few if any fertile flowers-- the typical broad four-petaled flowers are in fact sterile, but our native Hydrangea sports a broad umbel of tiny, spiky fertile flowers at the center, surrounded by showier sterile structures.