When we were in P'yatikhatki on Thursday, Volodya gave us some unusually large walnuts from his tree. They are huge relative to the normal ones from our trees, with thick highly convoluted shells (if that is the right word). The meat inside is more than from our normal walnuts but not as much more as one would think from the size of the nut.
Planting them results in a tree that yields normal walnuts. Puzzel for the day.