I have had a bunch of radishes going wild this year that re-seeded
from last year. All of them looked the same, with the bulbous root
and the lanky stem, the typical leaves, and the white flowers.

Until this came along:

http://i868.photobucket.com/albums/a...s/P1170634.jpg

http://i868.photobucket.com/albums/a...s/P1170636.jpg

The leaves and flowers and color are all the same as the others, but
its stem is about three times the thickness of that of any other
radish plant I have. It's so thick it's begun to crack. Is this a
mutation? The result of odd pollination? Not a radish at all?