Rhizome

A rhizome is a horizontal underground stem that produces aerial shoots and roots at intervals along its length. Cattails, torpedograss, and many shoreline emergents reproduce primarily by rhizome extension rather than seed. Rhizomes accumulate stored carbohydrates that allow regrowth after surface cutting — which is why mowing only the visible cattail tops produces denser regrowth. Cutting below the waterline drowns the cut stalk and forces the rhizome to deplete its stored energy on a regrowth that also drowns.