Oh man, these are looking great around the arboretum pond, where the pickelweed used to be in bloom. My height, with showy blossoms about 6 inches across. This is also growing in the local river marshes alongside the purple loosestrife for a major show. Native.
Swamp Rose Mallow, Rose Mallow (Hibiscus moscheutos)
Bonus picture: if you turn around from photographing the mallow, you see Matt, who came for tai chi class and then stayed to add ambience to the arboretum.