Dear Gargji:
This aquatic marsh plant species was found growing submerged in a mountain stream of Shyadri hills. Most of the plant seems to be covered in yellow inflorescence, this seems to be endemic to a particular valley. In addition there is an aromatic odour( like Limnophila aromatica) on pinching the flowers. The leaves resemble Limnophila, plant seems to survive summer by deep rhizome.
This was reminiscent of Pilea microphylla but very different on closer inspection.
Request for an Identification.