Potamogeton crispus aka Curled Pondweed

Potamogeton crispus is a submerged aquatic perennial in the Potamogetonaceae family. Its common names include curled pondweed and curly pondweed. It is native to the Old World, including Britain and Ireland. Its broad range covers Europe, Asia and Australia. It grows in lakes, ponds, streams and canals. Records place it in both fresh and saline water.

The leaves stay below water rather than floating on top. They are narrow and lance-shaped, or more oblong in outline. Mature leaves have strongly waved edges, which explain the common name. The foliage is deciduous, so it does not remain year-round. Small reddish flowers appear in summer but make little visual impact. The RHS gives a garden height of 0.3 feet [0.1 metres]. Its listed spread is much wider, at 3.3–4.9 feet [1–1.5 metres]. Plants take five to ten years to reach their full size.

This pond plant grows in full sun or partial shade. The RHS recommends baskets filled with sandy loam, set in pond-bottom mud. It accepts acid, neutral and alkaline conditions. Its listed soils include both sand and loam. Water is central to its care; this is not a dry-ground plant. The RHS rates its hardiness as H7, its coldest category. That rating covers severe continental winters with temperatures below −20°C. The planting guidance allows either exposed or sheltered sites. It also lists sites facing any compass direction.

Its garden role is as a submerged plant for ponds. Much of its form sits beneath the water surface. The waved leaf edges give it its main visual character. The RHS includes it among plants needing little routine care. Even so, regular thinning helps keep its spread in check. Plants For A Future also flags its potential to become weedy. Stem cuttings offer a way to raise more plants. Take them from mid-spring through early summer. The RHS reports few usual pest or disease problems.

Plants For A Future lists cooked young leaves as edible. It also lists roots, but gives no preparation details. Its food-use rating is two out of five. The same source reports no known hazards. That statement does not amount to a full safety assessment. It records no known medicinal uses or other practical uses.