Most folks just cutoff the stem near the base. I believe this promotes more leaves at the bottom. Sometimes the stems at the surface will form into floating oval leaves (particularly if the water is still and the lighting is decent). If you want to propagate the plant then cut the stem about 2-4 inches from the oval leaf and let it float in the tank. In a few days new roots should develop and it can be replanted when the roots have increased in size and number.