The plant has leaves in opposite pairs along a creeping hollow stem, with nodes 5 - 10cm apart. Fibrous roots may be reproduced from the stem, which reach down into the water or soil. Soil roots are often longer and thicker than those in water, often extending to below 50cm in depth.
Nodes also produce shoots that can produce new plants.
The stem of the plant is green-brown but often redtinged. Alligator weed leaves are hairless, waxy and green and have a conspicuous midrib. They are 2 to 7cm long and 1 to 2cm wide. The white flowers resemble those of a clover but are smaller and each cluster is produced on a long stalk. The plant grows best in fertile, nutrient-rich conditions and requires a warm growing season although it doe s tolerate cold winters.