Tree

A tree was a wooden plant which was often rooted into the ground. An area of multiple trees was called a forest.

Biology
Trees were often made of wood and had leaves. You could tell their age by the number of rings across the insides of their trunks. (TV: In the Forest of the Night) According to the Rani, a tree had four times the life expectancy of a human being. (TV: The Mark of the Rani) As they grew, trees could mangle fences and topple structures, as they did Nelson's Column. (TV: In the Forest of the Night)

While the majority of trees were rooted into the ground, some were able to move and claimed sentience. (TV: The End of the World)

As a natural resource
Androzani trees were used as fuel by the populace of Androzani Major. (TV: The Doctor, the Widow and the Wardrobe)

As decoration and comfort
At Christmas, some trees were decorated with lights and baubles. (TV: The Runaway Bride) Town planners on Tivoli used trees to provide shade for invading armies. (TV: The God Complex)

History of trees on Earth
Whilst on Earth in the 1820s, the Rani mined a section of forest with mines that turned humans into trees. Following their transformation the former-humans retained some level of consciousness. (TV: The Mark of the Rani)

In 2016, a global forest grew overnight to protect the Earth from a solar flare. The forest was able to communicate with Maebh Arden. (TV: In the Forest of the Night)

Types of trees on Earth
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Elsewhere in the Universe
The forests of Eden were dense even in the small section captured by Tryst's Continuous Event Transmuter. (TV: Nightmare of Eden)

Vislor Turlough once described the trees on Trion as being three times the size of Earth trees, with plate-like thick mauve and purple leaves growing in spirals up blood-red trunks. (AUDIO: Loups-Garoux)

Calderon Beta was home to a four hundred foot tall tree "growing out of a clifftop on the north side of a mountain in the middle of the sea". (HOMEVID: First Night)

A species of tree existed on Gallifrey with silver leaves. These reflected the morning sunlight, making it look like the forests were on fire. (TV: "A Desperate Venture", Gridlock) There were also green forests, similar to those on Earth.

In the year 5345, the Eleventh Doctor encountered a group of Androzani trees who were attempting to flee their doomed homeworld. (TV: The Doctor, the Widow and the Wardrobe)

By 5,000,000,000 many trees that had originated on Earth had achieved sentience and humanoid form. (TV: The End of the World)

The Sixth Doctor and Frobisher encountered a talking tree while in Astrolabus' realm. (COMIC: Once Upon a Time Lord)

Miscellaneous trees
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