Rose of Sharon, also known as the Hibiscus tree, Hibiscus rosa-sinensis.
Photographed on Columbus Avenue, between West 81st and 82nd streets.
Hibiscus rosa-sinensis is one of many plant genera that can exhibit polyploidy, a condition where its number of chromosomes is far greater than the two sets that come from each parent. Polyploid offspring can have very different morphologies from either parent, or indeed any ancestor, due to random expression of any or all of the characteristics present in its ancestors. Because of this characteristic, H. rosa-sinensis is popular with hobbyists who cross and recross varieties, creating new named varieties and holding competitions to exhibit and judge the many resulting new seedlings and often strikingly unique flowers.
When I and my mother were still living in New York (she was out on Lawn Guyland), Mom had a couple of Rose of Sharon trees in the back, but not with flower colors like that -- one was pink, the other white with red markings. I remember being told that they're quite invasive.