Pumpkin

Pumpkins were a type of vegetable traditionally carved into jack-o'-lanterns for Halloween. The heads of the Hervoken resembled carved pumpkins. (PROSE: Forever Autumn)

History
Before humanity developed on Earth, a damaged Hervoken ship crashed into the planet, embedding itself in what would later be New England. The Hervoken slept for thousands of years while a tiny speck of their consciousness influenced humanity to perceive the Hervoken as legends. Through this, it became traditional to carve faces into pumpkins so that they resembled Hervoken.

Around the time of the formation of the United States of America, the town of Blackwood Falls was built on top of the crashed Hervoken ship. It became a tradition in this town to burn a scarecrow with a pumpkin head each year at Halloween to ward off evil spirits (PROSE: Forever Autumn)

In the late 20th century, pumpkin pie was in the Christmas dinner provided by the Los Angeles Midnight Mission. (PROSE: Goodwill Toward Men)

In 2008, the citizens of Blackwood Falls decorated their front porches with jack-o'-lanterns. Many shops, including Tozier's Costume Emporium, also decorated their storefronts with carved pumpkins. Pumpkin pie was served at the Halloween Carnival. (PROSE: Forever Autumn)

On the Halloween in which the Cerebravores attacked New York City, one trick-or-treater dressed as a vampire had a basket that looked like a pumpkin. (COMIC: Revolutions of Terror)

When Zargofly and Zarkon tried to invade Texas, the Eleventh Doctor and Amy Pond harvested and carved pumpkins into jack-o'-lanterns to trick them into thinking that humans cut off and hollowed out the heads of their enemies. (COMIC: The Trick)

Other references
The Seventh Doctor observed that "the proof of the pumpkin's in the squeezing" as he asked to check Melanie Bush's pulse to prove she was not the Rani. (TV: Time and the Rani)

When the Eleventh Doctor, out of bed looking for a midnight feast, asked Alice Obiefune what happens at midnight, she flippantly guessed that "[he turned] into a pumpkin". (COMIC: Midnight Feast)