I'm from South India and I'm having quite a fuss identifying this plant.
It has totally transparent stems, and when I break them, water squeezes out. My local friend tells me that this was used in the olden days to clean slates. It has a bit fat stem. And another thing about this plant is that when you soak it in Ink, you can see the ink travelling up it. That's why it is so transparent.
I heard that it is locally called Mashithandu and I searched all over the net for it, but can't find a name except that. I'm really sorry I can't add a photo. I'll see what I can do.