Cactus

Cactus was the name given to several varieties of desert plants found on Earth and other worlds, which were usually green in colouration and covered with pointed spines.

The Zolfa-Thurans were similar in appearance to cacti. (TV: Meglos)

Wilfred Mott likened the Vinvocci to cacti due to their spiky green faces. Such a remark was apparently racist. (TV: The End of Time)

In Aztec Mexico, Ixta slashed Ian's wrist with a cactus needle the First Doctor had given him for a fight. Ian's energy was drained by this. (TV: "The Warriors of Death")

Jack Harkness once called Gwen Cooper "Cactus Woman", because she was being "prickly". (PROSE: The Wrong Hands)

When Amy Pond and Rory Williams stopped by the Old West on their honeymoon, Rory had a "cactus accident" which prompted Amy to ask the Eleventh Doctor to bring them some Salvon when he came to pick them up. (PROSE: Honeymoon Horrors)

References in invalid sources
Dennis the Menace once used a cactus for "target practice", by launching the spikes off of one and into a police officer's posterior, which his dog, Gnasher, had painted a red target onto. (NOTVALID: Dennis the Menace in Balloonatics)