Their bodies are only 2.5 mm across. Their bodies are green above and purple below. They rarely produce flowers but, when they do, the flowers are tiny and white. The tiny flowers are either male or female but not both as in most flowering plants. The flowers are tiny with either a single anther or a flask-shaped ovary.
Great duckweeds produce most new plants by budding.
A tiny bump grows on the green body and sends down tiny roots. The bump then pinches off to make a new plant. Each duckweed has two or more hairlike roots that hang down in the water. The roots absorb minerals directly from the water. A mass of tiny roots from thousands of great duckweeds, forms a micro-habitat for algae, water fleas and microscopic animals.