Potatoes were a vegetable on Earth, and is used to make other Earth food like chips.
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)
The Sontarans were said to look like potatoes on several occasions. (DW: The Two Doctors, The Sontaran Stratagem, SJA: Eye of the Gorgon)
