my, it looks like one of the sweet potato tubers but its not a sweet potato. Have you tried going to the asian supermarket? If you can find a tuber, it should be easy to grow from that.

Ianna, I don't think it will grow from that part of the tuber, but from the new growths just under the crown where the eyes grow Like in the link below. I think the tubers sold for eating are minus these.
Annette

Here is a link that might be useful: Yacon

well absent of being able to obtain one from a supplier, why don't you give the grocery one a try anyway. Many tropical types will grow from all sorts of tissues. It just may work.