Oak

You may be looking for the engineer or the Gardener.

An oak was a tree native to Earth. Its Latin name was Quercus robur. (PROSE: The Secret in Vault 13)

The Fourth Doctor claimed that oak trees didn't grow anywhere else in the galaxy. (TV: The Android Invasion) As River Song explained, botanists had tried to seed them on other colony planets, but they always died. (AUDIO: The Unknown) The Master however proved able to seed oak trees on Destination. The sight of them led Susan Foreman to believe that they were on Earth. (AUDIO: The Destination Wars)

For thousands of years, the Centuripedes used the oak trees of Earth to build pods to transport their eggs. (TV: The Last Oak Tree)

In the 12th century, an oak tree known as Major Oak was used by Robin Hood and his merry men as their sanctuary. (TV: The Last Oak Tree)

Some time before the 18th century, an Ambition Parasite came from Esto to Earth and infested an oak tree. (PROSE: Number 1, Gallows Gate Road)

In the 1970s, Styggron's replica of Devesham included fake oak trees. (TV: The Android Invasion)

Acorns from Robin Hood's time. (TV: The Last Oak Tree)

By 2050, oak trees were extinct (at least in England), all having been cut down or died of pollution. The last oak tree, Major Oak, was kept on display in a museum in London. This tree was stolen by a Centuripede and used to build a pod for her eggs. After Starkey and K9 helped save her eggs from Drake's bomb, she rewarded them by saving their lives and giving them the acorns she had saved from Robin Hood's time. (TV: The Last Oak Tree)

Anzor's TARDIS once took the form of an oak tree. (AUDIO: Mission to Magnus)

Oak trees were also found on Tír na n-Óg, having been taken there by Goibhnie. (PROSE: Cat's Cradle: Witch Mark)

A forest on a Ch'otterai's planet had oak trees growing in it. (PROSE: The Mystery of the Haunted Cottage)

While trying to work out how a forest had grown on Earth overnight, the Twelfth Doctor compared a tree to a time machine, and determined that this had to have happened due to messing with the fabric of time, as "you [couldn't] create a whole overnight forest with extra special fertiliser". He referred to a hypothetical scenario, where "[y]ou plant[ed] a little acorn in 1795, and in the year 2016, there [was] an oak tree, there in the same spot, with a tiny, little bit of 1795 still alive inside of it." (TV: In the Forest of the Night)

River Song once told the crew of Saturnius that oak trees were unable to thrive on other worlds despite many colonists having tried to cultivate them. (AUDIO: The Unknown)

An oak tree was planted at Coal Hill School in memory of Ian Chesterton and Barbara Wright. Surviving two Dalek invasions, it remained to at least the end of the 22nd century when it was found by Susan Foreman, who lived in the block of flats which Coal Hill had been converted to over a hundred years prior. (AUDIO: All Hands on Deck)