Q. We had a beautiful purple locust in our back yard that produced a profusion of purple flowers every spring until it was called to locust heaven. Before departing this world it sent off a runner which has sprouted into a lovely tree that is now eleven feet tall and producing white flowers. What’s with that? A. I am making a lot of assumptions in answering this. I am assuming what you are seeing is a locust and not some other plant that happened to grow in that location. I am also assuming the flower looks exactly the same as the purple one, just that it is white.             If both of these are correct then you are seeing the rootstock suckering. The rootstock used for producing the locust with purple flowers is a black locust. Black locust has white flowers but otherwise looks identical to the purple locust.             Oftentimes the locust that has purple flowers is grafted onto a black locust rootstock. The purple part of the plant dies. Suckers grow from the roots of the black locust rootstock and have white flowers.