Dig down very carefully around the base of a plant that you think is a "normal" plant and see if you find a root that would extend from the mother plant to the new plant several inches away (if you can find one). Then do the same with a plant that is four or five inches from the mother plant (one you feel sure is a rhizomatous plant) and follow the root from the mother plant to the new one. That will give you a better idea of how a rhizomatous plant spreads. Most plants do not spread by rhizomatous roots, some do and they are not aggressive with their spreading. Others want to take over the entire daylily bed.
