Callery pear crosses with common pear, producing a swarm of hybrids. Among the ones seen near here is a tree with round fruit about one and a quarter inch across. These taste like an apple pear cross, and are slightly firmer than a common pear. Another has fruit that look exactly like Chinese pears from the market. But these are so hard that they lay on the ground for weeks with only a few tooth marks from wildlife. Another has fruit just like common pear, but only an inch and a half long. Yet another is completely sterile, not even producing flowers. In the posted image, the stamens are still curled up in the position they were in inside the buds. You can see the two pistils of Callery pear in the center. Common pear has five pistils. One way you can know you're looking at a hybrid in flower is that there will be three or four pistils. The image here is from Tennessee, where Callery pear had colonized a lot next to our lunch stop.