Sunflower

Sunflowers were a plant species unique to Earth. (AUDIO: Caerdroia)

Amy Pond gave many sunflowers to Vincent van Gogh as a gift for saving her from the Krafayis. (TV: Vincent and the Doctor)

Face-Painter once painted a sunflower on the Second Doctor's face. (PROSE: Face-Painter)

The Tenth Doctor once reprogrammed a want conduit to only work when the user thought about sunflowers and ball bearings. (PROSE: The Slitheen Excursion)

Grave Diggers used sunflower-based flamethrowers. (PROSE: The Secret in Vault 13)

Sunflowers were grown in their garden in Spiral by a survivor of Dawn 10000. The fact that they pointed away from the Sun allowed Coloth to realise that they were inhabited by the beings of light and were instead pointing the way to a portal back to their home universe. (PROSE: Sonnenblumen)