So the sort of turnip that has a root below the bulb, or at least hasn't had it cut off. This entry is brought to you by the Department of There Really Is A Word For That?. This is mostly used only by botanists, and not surprisingly was coined by them around 1841 from Latin roots nāpus, a type of turnip, from Greek nâpu, a type of field mustard (if you've ever eaten turnip greens, you'll know why this makes sense) + -form, shape of. Turnip is, incidentally, descended from the same Latin word, with turn- added on front because of the round shape as if turned on a lathe.
Without a beard, his face was surprisingly napiform.