Trapa incisa

Trapa incisa is a water plant in the Lythraceae family. It is an annual, so it lives for one year. Its native range spans northeast India to the Russian Far East. It also grows in temperate East Asia and parts of Southeast Asia. Records come from China, Japan, and Korea. They also include Myanmar, Thailand, Laos, Cambodia, and Vietnam. Most of its range has a subtropical climate. In Japan, it grows in lakes and ponds. These sites lie in the country's central and southern regions.

The plant has a stem below water and leaves that float. The leaves form a rosette at the water's surface. Its swollen leaf stalks, or petioles, help it float. It grows in shallow water, in ponds and swamps. The supplied sources give no sound mature height or spread. Nor do they give much detail on flowers or fruit. The flowers have both male and female organs. The plant can use its own pollen to set seed. Insects also bring pollen to its flowers.

In gardens, this species needs water, not a dry bed. It suits ponds where water stays still or flows slowly. Give it full sun; it does not grow in shade. The sources call for water with a slight acid level. They also call for a rich mix to plant in. Plants For A Future lists sand, loam, and clay soils. It gives a soil range from mild acid to neutral. Warm summers help the plant grow well. Frost kills plants while they grow. Seeds, though, can live through freezing winters. Whether it is hardy outdoors in Britain remains unclear.

People gather seeds from wild plants to eat. They also grow this species for its edible seeds. The sources say to boil the seeds before eating them. They do not show whether this species' raw seeds are toxic. This evidence thus supports no safety claim for this species. Plants For A Future rates its food value as low. It lists no known uses as medicine or for other ends. A pond is the stated garden setting for this plant.

To grow new plants, collect seeds in late summer. Keep them wet, as drying soon harms their chance to sprout. Store them in water through winter somewhere cold but frost-free. Sow in spring, with one seed per pot below water. Useful Tropical Plants reports a 2013 IUCN assessment of Least Concern. It says the species grows widely in China and Southeast Asia. It reports no specific known threats.