Warning! As is discussed in the comments to the answer, the plant and tuber may be poisonous and must be cooked by experts.
I went to a village market in NE Thailand. They had many products from "the jungle". For lunch I had steamed, shredded coco-nut, pumpkin and a white tuber (?) they called "glooi". I assume the "glooi" is sliced (and steamed) in the picture below.
Does anyone know more about "glooi", it's English name etc?