Crataegus monogyna, or common hawthorn, is a less well-behaved plant that is decidedly invasive in the western states of Oregon, Washington, and California, as well as some areas of the Northeast U.S. These species are quite hard to tell apart, but C. monogyna is usually a larger plant, with leaves that are narrower. C. laevigata, by contrast, has leaves that are wider than they are long. Further complicating the issue is that these plants readily hybridize—both with each other and other hawthorns. It's best to buy your plant from a reputable nursery to ensure you are not planting an invasive species.