Alisma gramineum, commonly known as narrowleaf water-plantain or ribbonleaf water-plantain, is a perennial aquatic herb native to temperate and subarctic regions of Asia, Europe, North Africa, and North America. It is typically found in shallow fresh or brackish waters such as marshes, ponds, and slow-moving streams. In its native habitat, this plant is an important component of wetland ecosystems, providing habitat and food for aquatic wildlife. Alisma gramineum reaches a height of 15-30 cm and has a spread of 10-20 cm. It features narrow, ribbon-like submerged leaves and small, inconspicuous purple-tinted white flowers that bloom above the water surface in summer. The flowers are cleistogamous, meaning they self-pollinate without opening, which occurs underwater. This plant also produces emergent flowers that are pollinated by insects.

Narrowleaf water-plantain is valued for its ability to oxygenate water and provide cover for aquatic organisms. It is used in water gardens, natural ponds, and for aquatic restoration projects. It prefers shallow, nutrient-rich water at the edge of bodies of water and fenland drains, and it requires full sun to part shade conditions. While it reproduces by seed or division of the corm, it is considered endangered in the UK, with known populations in Worcestershire and Lincolnshire. Gardeners should be aware that although it is not typically invasive, it can spread in ideal conditions, potentially outcompeting other aquatic plants.CC BY-SA 4.0