S. reticulata. Creamy white blooms get very large and showy over time as does the tree-like shrub. 24-40 feet tall if left unpruned. Zones 2-7. If you wish to see how large Japanese Tree Lilacs can grow,  coming into Plainfield, Vermont from East Montpelier on Route 2 on the sharp corner just before the signs for Goddard College and Rt 215, the road is lined with them.  The extra-large braches hang over the road, occasionally struck by tractor-trailers. The fragrance of so many in such a small area is noticeable coming from either direction long before you get there.