Dear Saroj,
I'm definitely leaning to Colocasia fallax here. The oblong stigma and overall inflorescence structure point to this.
In your photo the stigmas appear to be at peak receptivity, so rather swollen compared to the very sketchy sketch of an oblong stigma in the paper's figure. I have not seen brown stigmas like this before, and have not seen mature inflorescences on
C. fallax, so don't know if this is typical or not.
Your photos show a partially buried plant and the inflorescence emerging from sand. I suppose this is just a chance result of erosion in a gully or along a stream bank, not a peculiar subterranean habitat!
The stolons of C. fallax have a remarkably strong inner fibrous core, and are a little like the cables used to hang suspension bridges... I suppose this is part of it's adaptation to rocky stream courses and gullies with high-energy seasonal water flow.
Best regards, Peter