We were given a box of vegetables as a New Year present.* The things pictured were included in it. Not know what they were or how to cook them, we decided that boiling worked for most things, and put them in a soup. They were delicious.
I managed to find out what they are from Google, and found to my surprise that they are water chestnuts. I've had them before, but only as tasteless crunch in stir-fries. Frankly, I wondered why anyone would bother with them. Fresh ones, however, are completely different - they have a floury texture and subtle taste, rather like potatoes.
*Judging by what's on offer in the local supermarket, acceptable New Year gifts include, but are not limited to, boxes of fruit, coffee, and thermal underwear.