That's what they do, the leaves die and float away.
I purchased them from a member of this site, I don't recall what they are - one of them is Indian fern - that seems to be doing well in my fighter's tank, possibly because it's near the heater?
The fighter's tank is about 40 litres and has a 9W double bulb, the colour is red (good for plants apparently) but I also have white. I planted some baby plants on a log but they all died. Also another long plant which seems ok so far, the odd leaf has died though.
The community tank is the worry, the water went green due to too much nutritian (whatever that means) and not enough plants. Some plants were floating but looked very scody and another is a floater - like a mossy grass, that I tie down to cover stones - that's still ok but lots of it is all over the floor of the tank now. That tank has a pink/red bulb and I turn my tank lights on the evening for a few hours (up to 3 hours maybe).
Admittedly the dollars ate most of the plants, but they still looked crap even before the dollars got at them and it didn't take long for the water to turn green.
I tried plants years ago, and the same thing happened then - water turned green, plants dying - gave up then and maybe I should give up now, would really like a planted tank though.