Psychic mushroom
From Tardis Wiki, the free Doctor Who reference
Psychic mushrooms are formed due to psychic paper mouldering. The psychic mould would eventually turn into psychic mushrooms.
Inside of the TARDIS Library (during the time of the Tenth Doctor), there was a specific desk that, no matter where it was moved, always got rained on by a cloud layer in the upper stacks. The Doctor placed a saucepan on the desk to catch the water and keep psychic paper from mouldering because it produced psychic mould that would eventually turn into psychic mushrooms.
