There is a small reservoir in area of my taking walk, ten minutes on foot from my house. In early summer, some tiny leaves appear here and there on the water surface. And each time I walk by, I notice that water space of the reservoir gets narrower with these leaves which grew in size and increased in number. They are leaves of Trapa japonica, Hishi in Japanese.
I myself, have never noticed this plants bear nuts on the reservoir near my house, and just after the flowers bloom, they seem to fade and sink to disappear. In fact it looks that the fade-out is quicker than the growing, as I have seen in these years that after several days of their zenith their green colour turns to darker and suddenly on some day I can observe nothing but water there.
The way of growing and fading of Trapa japonica is supposed to be opposite to that of freezing and of making sheet of ice on a pond; ice sheet is made almost in a day or so and melts little by little taking time, in some cases the parts of melting ice look like the leaves just after appearance on water as the photo shows, on the contrary Trapa japonica grows day by day and vanishes almost abruptly.