Water chestnut
Family Trapaceae
Trapa natans, the water chestnut (T. natans 1), is an aquatic plant from the Old World, with submerged and floating leaves, the last ones with spongy swellings in the petioles. The flowers are small, solitary and white, with 4 petals and 4 stamens. The triangular sepals fuse with the ovary and form horn-like projections. The fruit is a nut, the water chestnut, which has been used for food since Neolithic times.
Use
The fruits (T. natans 2) are used boiled, tinned, preserved in honey and sugar and used for making flour.