Turnips were a common vegetable found on Earth.
Peri Brown once found herself in a dimension modelled upon a combination of the Alice in Wonderland book she had been reading and the salad she had been eating. Among the creatures she met in this world was a pair of talking turnips reminiscent of Tweedle Dee and Tweedle Dum. (COMIC: Salad Daze)
A mixture of turnips with molasses and potatoes was once used by the Tenth Doctor to clog up proton cannons being fired upon him and Martha Jones. Having landed aboard an American schooner in the Caribbean Sea during the Quasi-War, the time travellers had to quickly prepare the mixture to thwart their attackers. The mixture gunked up the cannon's intake valve and immediately caused it to explode. (COMIC: Second Wave)