Leaf

A leaf was a component of plants and trees.

Biology
Leaves grew on plants and trees. On Earth, during the autumn, dead leaves would fall to the ground. (TV: The Rings of Akhaten)

While Earth's trees had green or orange leaves, other planets had leaves of different colours. The Cadonwood trees of Gallifrey had silver leaves, as did the trees native to Fragrance. (AUDIO: Neverland, AUDIO: The Fragile Yellow Arc of Fragrance) The Time Trees of Hirath had orange leaves and the Poppito trees of Raxacoricofallapatorius had reddish-brown leaves. (PROSE: Genocide, PROSE: The Monsters Inside)

As trade goods
Tea plants had leaves, which were used to make tea. (TV: The Awakening)

As drugs
Certain types of leaves had medicinal properties and some could be addictive. Raspberry leaf tea was good for the ailments of the throat. (TV: The Sun Makers) Tobacco leaves were used in making cigarettes. (PROSE: History 101)

As superstition
Superstitious people believed that leaves could bring luck or be used to tell the future. Some clovers had four leaves, and were considered lucky. (COMIC: Triskaidekaphobia) Tea leaves were read by psychics to tell the future. (TV: The Curse of Clyde Langer)

As a weapon
claimed she once built a gun out of leaves. (TV: The Lie of the Land)

History of leaves on Earth
In 1981, a leaf dubbed "the most important leaf in human history" brought Dave and Ellie Oswald together. Their daughter Clara kept the leaf as a keepsake. (TV: The Rings of Akhaten)

Alternate Earths
In a dream created by the Dream Lord, Rory Williams at first mistook the sound of the TARDIS materialising for the sound of someone blowing away leaves with a leaf blower. (TV: Amy's Choice)

History of trees on other planets
While on a colony built entirely on one giant tree, the Eleventh Doctor and Amy Pond once used a giant leaf as a parachute when escaping the Pulpavores. (COMIC: The Evergreen Death)

The Sixth Doctor kept a cabbage leaf in his C chest. (AUDIO: The Carrionite Curse) The floor of the TARDIS Cloister Room was covered in dried leaves. (TV: Doctor Who)

On Susan Foreman's home planet, there were trees with silver leaves. (TV: The Sensorites, PROSE: The Sensorites) The Tenth Doctor later mentioned that Gallifrey had trees with silver leaves. (TV: Gridlock)