Trapa bicornis @ Mid-Autumn Festival

菱角 The water caltrop is the seed of an annual aquatic plant, Trapa bicornis of the family Lythraceae. The generic name Trapa is derived from the Latin word for “thistle”.

Biology

The water caltrop’s submerged stem reaches 12 – 15 ft in length, anchored into the mud.

It has 2 types of leaves : finely divided feather-like submerged leaves borne along the length of the stem ; and undivided floating leaves borne in a rosette at the water surface. The floating leaves have saw-tooth edges and are avoid or triangular in shape, 2 – 3 cm long.

4-petalled white flowers form in early summer and are insect pollinated.

Fruit is a nut, barbed spines. Seeds can remain viable for up to 12 years.

Economic Importance

Native to warm temperate of Eurasia and Africa, it has been cultivated in China and India for at least 3,000 years. The seeds, which after boiled are consumed as snack or medicine.

It was introduced to North America around 1874, escaped cultivation and become an invasive species in Florida, North Carolina, and Washington.

In Australia, it is declared a noxious weed in the state of New South Wales.