Ceratopteris thalictroides aka Water Fern

Ceratopteris thalictroides is a water fern called swamp fern or water sprite. The RHS also lists the names pod fern and water fern. It belongs to the Pteridaceae family. Its native range spans the tropics and subtropics. It is not native to Britain or Ireland. This fern grows in water or in wet soil. Plants may root in the bottom or float at the surface.

The listed height is about 2.3 feet [0.7 metres]. Taller plants can reach 3.3 feet [1 metre]. Its form changes with growing conditions. Under water, its sterile fronds have fine, narrow leaf segments. These leaves are three or four times pinnate. Wild plants may gather around logs and mats of floating plants. Growers use it as an aquarium plant under the name water sprite. People also grow it in gardens as a food crop.

In the wild, it grows in swamps, marshes, and swamp forests. It also lives in both natural and built ponds. It favours still water, including quiet areas beside slow rivers. Most sites lie in the lowlands, though some occur higher up. In cultivation, it grows in full sun through moderate shade. It prefers temperatures of 20–22°C and a pH of 5–6.5. Plants can float freely or grow in shallow water. The stated water depth limit is about 1 foot [0.3 metres].

This fern can complete its spore cycle in under 30 days. Growers can raise new plants from spores or leaf bulbils. Pieces of leaf left floating can also form new plants. These methods offer several ways to increase aquarium or food plants. Its use as a vegetable is well established in parts of Asia. People harvest young fronds before the leaves fully unfurl. They eat them raw or cooked, including blanched leaves in salads.

Useful Tropical Plants records no reports of poisoning from this species. That statement does not establish that every use is safe. The same source records traditional medicinal uses for several plant parts. People apply leaves and roots as poultices for skin complaints. In China, they use the plant to help stop bleeding. The source also records remedies made from rhizomes and fronds. These are reports of traditional use, not proof that treatments work.