Salvinia, perhaps?

http://agnews.tamu.edu/agex/salvinia.html



David Hare-Scott wrote in message
...
Please help me identify this freshwater aquatic plant. I am trying to
get a picture but so far not available.

The plant floats with stem segments about 2" (50 mm) long, the top of
the leaves are above the surface and they are dense on the stem with
very short stalks so only the leaves are visible from above. The
underside of the segments have a mat of dark greenish roots hanging down
about 1/2" (12mm) to 1" (25mm).

The leaves are oval, a uniform bright green about 1/2" (12mm) long and
2/3rds of that wide. The leaves occur mainly in pairs on the stem, each
leaf has a crease down the centre in line with where it is attached to
the stem so that the top is slightly concave. The upper surface is
covered with short hair-like protruberances and sheds water. The leaves
feel soft and fleshy to the touch.

David