Glyceria fluitans, commonly known as floating sweet-grass or water mannagrass, is a perennial grass native to a variety of wetland habitats including marshes, ditches, riverbanks, and pond margins across Europe, the Mediterranean region, and Western Asia. It typically grows to a height of up to 3 feet (0.9 meters) with creeping rootstock that allows it to spread effectively in its native environment. The plant features long, narrow, pale green leaves that are rough on both sides and often folded along the central vein, or keel. Flowering occurs in the summer, producing a loosely branched inflorescence that is not particularly showy.

Floating sweet-grass is valued for its ability to stabilize soil and water edges, making it useful for erosion control in wetland restoration projects. It is also appreciated for its historical use; the sweet grains were once harvested to make a gruel. However, its potential for invasiveness should be considered before planting, as it can spread aggressively outside its native range. In cultivation, Glyceria fluitans requires consistently moist or wet soil and can grow in full sun to part shade conditions. It is not particularly drought-tolerant and may require additional water during dry periods. While it can be a useful plant for specific purposes, it may become problematic if not managed properly, as it can form dense mats that outcompete native vegetation.CC BY-SA 4.0