Zannichellia palustris aka Horned Pondweed

Zannichellia palustris is a submerged perennial called horned pondweed. The RHS places it in the family Zannichelliaceae. It is native to Britain and Ireland. Plants For A Future describes its range as almost worldwide. Its listed range spans Europe, temperate Asia, and North Africa. These records include Nordic countries and lands around the Mediterranean. It grows in fresh water and also tolerates brackish water. Its habitats include still pools and water with a slow flow.

This plant reaches about 1.6 feet [0.5 metres] in height. It lives beneath the water rather than on dry ground. Flowers appear from May to July. Each flower is either male or female. Both kinds grow on the same plant, a condition called monoecious. Water carries the pollen between flowers. The supplied sources give no further details about its foliage or fruit. Its value in a pond rests on its submerged growth and water-related uses.

Horned pondweed suits cool-water ponds, where it acts as an oxygenator. It grows in full sun or partial shade. Sand, loam, and clay all fall within its soil range. It accepts mildly acid, neutral, and mildly alkaline conditions. It can also grow in saline soil. These broad tolerances suit its fresh and brackish water habitats. PFAF lists it as hardy to UK zone 2. That source does not supply a matching RHS hardiness rating. Its need for water remains central to any planting site.

Beyond pond planting, this species has other practical uses. PFAF reports that it helps hold muddy banks in place. It also records a role in cleaning polluted water. Division offers a means of making more plants. PFAF says division is easy through most of the growing season. Its seed guidance is less certain and presented as a suggestion. It proposes sowing ripe seed in pots kept under water. It warns that drying may shorten the seed's useful life. Seedlings can move into separate pots before summer planting.

PFAF records no known food or medicinal uses for this species. It also lists no known hazards. That does not establish that the plant is edible. The supplied evidence names no pests or diseases. PFAF does not flag the species as weedy.