Potatoes were a vegetable on Earth, and is used to make other Earth food like chips.
The Sontarans were said to look like potatoes on many occasions. (DW: The Two Doctors, The Sontaran Stratagem, SJA: Eye of the Gorgon)
Sarah Jane Smith, when captured by Irongron, was put to work in his kitchen peeling potatoes. (DW: The Time Warrior)
The Doctor was once imprisoned in the Tower of London with Sir Walter Raleigh, who kept going on about the potato, which he'd discovered. (DW: The Mind of Evil)
