Frog-bit Hydrocharis morsus-ranae

When I was a kid in the 1950s nuclear power was the wonder of the age and the exploits of the nuclear submarine USS Nautilus, which was the first of its kind to traverse the North Pole underwater, was big news in the school playground.

To celebrate the event Kellogs cornflakes produced little plastic models of the submarine, that you could acquire by sending off a small fee and a tab from the packet to the manufacturers. You needed to fill the hollow submarine with baking powder, then it would sink and surface again when the baking powder became wet and released carbon dioxide bubbles. 

Kids were enjoyed simple pleasures in the pre-digital toy age.

The little plant in this photo emulates the actions of a submarine. It's frog-bit Hydrocharis morsus-ranae and it produces resting buds called turions that sink to the pond bottom in autumn then rise again in spring, like a surfacing submarine. 

The plant gets its name from the shape of those leaves which resemble that of a frog's mouth.

I've never seen frog-bit growing in the wild (it's very rare here in Durham) but several years ago I went into a shop in Leeds and found that they were selling the plant for indoor aquaria. I introduced it into my pond and it thrived alongside the frogs for a short while. A few turions rose to the surface again in the second year but after that it died out. I suspect that it was overwhelmed by dead leaves on the pond bottom or duckweed on the surface. 

Finding these old photos reminded me of the episode, and of the cornflake submarines. I notice that a few nurseries advertise the plant for sale so I might get hold of some and try growing it in a small aquarium. I wouldn't mind finding one of those toy submarines to play with too, for nostalgia's sake!