Yellow pond-lilies show up in every reference about plant lore. They are said to have been widely used as food and medicine. All parts of the plant are mentioned for food. But currently they're said to be too bitter to actually swallow. Modern studies do not support any of the many traditional medical uses. Two uses are agreed on. The plant, particularly the flowers, are very rich in tannin, and useful in that regard. And the seeds can be enjoyed like popcorn.