Potamogeton nodosus, commonly known as longleaf pondweed or Loddon pondweed, is a perennial aquatic herb native to a wide range of freshwater habitats including slow-moving rivers, ponds, lakes, and ditches across Eurasia and the Americas. It is particularly adapted to silty or muddy bottoms. The plant features a thin, branching stem that can extend over a meter in length. Submerged leaves are linear to lance-shaped, while floating leaves are shorter and ovate or elliptic, both types borne on long petioles. The inflorescence consists of a spike of small, greenish flowers that emerge above the water surface on a peduncle, typically blooming in the summer months.

Longleaf pondweed is valued for its role in aquatic ecosystems, providing habitat and food for aquatic wildlife. It is also used in water gardens and for natural water filtration in constructed wetlands. In cultivation, it requires a freshwater aquatic environment and can tolerate a range of light conditions, from full sun to partial shade. It is relatively low maintenance but may require control to prevent it from dominating smaller water features. There are no significant disease problems, but it can become invasive in some regions, outcompeting native species. Gardeners should check local regulations before planting.CC BY-SA 4.0