Help identify a strange root vegetable
Are you sure it was not in fact a puffball fungus?  There are some varieties that are edible and can be found in grocery stores.  Depending on how fresh, and when they were picked, they could easily be mistaken for a root vegetable.  Look for pear shaped puffball here for an example. http://www.wildernesscollege.com/edible-wild-mushrooms.html