Potatoes have rings.
Hello. I am going to forward your question to someone with more veggie experience than me.
Thank you for the picture, they always help. The plants have a virus. Most likely potato virus Y (http://blogs.cornell.edu/livegpath/gallery/potatoes/potato-virus-y/) but it would be hard to tell for sure without having it tested and I wouldn't bother to do that. Do not plant any seed pieces from this plant for next year's crop since the virus is transmitted in the seed piece. Most likely you got it from the potato piece you planted. It is okay to eat.