Here's one of the cultivated varieties. This is growing behind one of the older homes in Adrian, and has probably been there or nearby for a long, long time. Some varieties, even naturally, have a ring of flowers around the outside edge with much larger and showier petals. Those flowers are sterile. Pollinators have to visit the normal flowers to be rewarded. It is a floral bait and switch!
Common hydrangea was also called sevenbark. The bark peels, showing different colored layers. The plant was much used as medicine by American natives, particularly the Cherokee. They also peeled and fried the soft young shoots.