Alisma gramineum aka Alisma Graminoide

Alisma gramineum is a water plant in the Alismataceae family. People call it ribbonleaf or narrowleaf water plantain. It is native to temperate parts of the Northern Hemisphere. Its range spans parts of Eurasia and North America. The RHS lists Britain and Ireland as native sites too. It grows in marshes, ponds, ditches, and at lake edges.

This perennial lives for more than two years. Its thin, grass-like leaves grow in rosettes, or rings. Leaf shapes range from linear to lanceolate: narrow to lance-shaped. Some leaves stay below water; others rise above it. In gardens, plants reach about 1.6 feet (0.5 metres) tall. They spread about 1 foot (0.3 metres) wide. A wider reported height range is 0.5–2 feet (0.15–0.6 metres). The plant grows at a moderate rate. Short, thick rhizomes, or stems, form its starchy base.

Thin stalks bear small flowers in loose, branched sprays. Each bloom has three white or pale pink petals. The centres have a yellowish tint. After bloom, small fruits called achenes form in whorls, or rings. Bees and small flies visit the blooms. Some flowers may also use their own pollen to set seed. The plant adds cover and structure to shallow water. Its seeds and surface growth help support some waterfowl. They also support invertebrates, which are animals without backbones.

Grow it in shallow water with little or no flow. Its roots grow in soft mud or silt at wetland edges. Give it full sun, not shade. It grows in sand, loam, and clay soils. Its soil pH range spans mildly acid to mildly alkaline. It can also grow in moist or wet soil. Plants cope with some shifts in water level. PFAF gives a rough USDA hardiness range of zones 4–8. Grow it at pond edges or in pots filled with water. Sow seeds in mud under water, or split well-grown clumps. Cold, wet treatment may help seeds sprout.

The rhizomes can serve as food once cooked through. You can roast them, dry them, or make flour. Raw tissues hold sharp-tasting compounds that can cause irritation. You may need to change the water while cooking. Take edible parts only from wetlands free of contamination. This plant has limited worth as a food crop. PFAF lists no known medicinal use and no weed potential.