Mist-flower

Mist-flowers were flowering plants from the planet Sarkan. Once they flowered, they produced a dense fog. With enough of them, an entire planet could become enshrouded in fog, as had happened to Sarkan itself. The Master once tried to introduce the plant to Earth, starting in the seaside resort of Tadcaster, England. The Third Doctor and Joe discovered his cache of mist-flowers and buried them — along with the Master — in the sea. According to the Doctor, this would have killed the mist-flowers, as they couldn't "live in the sea". (COMIC: Fogbound)