Marsilea quadrifolia aka European Water Clover

Marsilea quadrifolia, or European water clover, is an aquatic fern. It belongs to the family Marsileaceae, not the clover family. Its native range spans Europe and Asia, reaching China and Japan. It grows in ponds, ditches, rice fields, and quiet waterways. Wet shores also provide a home for this plant. It loses its leaves with the change of season.

Long, branched rhizomes creep through the mud and form mats. Thin green stalks rise toward the water's surface. Each bears a dark green leaf with four triangular leaflets. The leaves measure about an inch across. Garden plants reach about 0.3 feet [0.1 metres] tall. Another account gives heights of 0.5–0.7 feet [0.15–0.2 metres]. The usual garden spread is 1.6–3.3 feet [0.5–1 metre]. Plants can take two to five years to reach full size.

This fern has no flowers and no flowering season. It makes spores within structures called sporocarps along its surface stem. Its low mats suit pond edges and bog gardens. Gardeners also grow it in aquaria and garden ponds. It can serve as ground cover beside shallow water. Both floating leaves and spreading growth shape its appearance. Sources flag weed potential, though they give no local impact details.

Grow it in wet loam with an acid or neutral pH. Full sun suits it, though it also accepts partial shade. Muddy pond edges offer a suitable planting site. Another option is a lattice basket filled with loam. Keep the planting depth within 0.5 feet [0.15 metres]. The RHS gives it a UK hardiness rating of H5. Missouri Botanical Garden lists USDA zones 6–10. Divide the rhizomes in summer, securing them in shallow water. It needs no pruning and has few reported pest problems. The sources also report little trouble from disease.

Young stems and leaves have served as food during shortages. PFAF rates its food value at one out of five. Reports also describe folk uses for fever and skin complaints. These reports do not establish that such treatments work. Food use does not mean the plant is risk-free. Useful Tropical Plants reports thiaminase in this species' sporocarps. This enzyme can deplete vitamin B1 and cause serious harm. That source says thorough drying or cooking reduces its amount. It does not say that heat always removes it fully. The same source reports a Least Concern assessment from 2011.