Years ago I moved into a house in Brisbane, Australia which had a large (12 ft high) retaining wall built of railway sleepers.
A vine started to grow on the wall, and after a while these large tubors appeared..... some hanging on the vine, others part submerged in the siol of the embankment. They were 3-4 inches diameter and about 12 inches long.
Not knowing what they were, I cut them off and disposed them (before the kids got "poisoned"???).
A year or so later, my wife remarked that they looked something like a sweet potato. So we cooked one up ......
And it was really tasty.... (i.e. we survived the taste test!)
The vine kept us in sweet potato for some years......
PS In Oz we use them like a potato (substitute), as a vegetable in roast meals, etc.
My wife says they are good for me........... (makes you wonder though.....)