The Trees of Cheem were humanoids with large, intricate heads, and wood-like skin. They had retractable vines on their arms called lianas, which they weren't supposed to show in public. The Trees of Cheem were made of wood, and were therefore highly flammable. (TV: The End of the World)
The Trees of Cheem did not understand technology, referring to computers as "metal minds" or "metal machines", but they were known to use it. They kept clippings of their relatives, occasionally giving them as gifts. According to the Ninth Doctor, they were of huge financial importance due to their land holdings and forests on various planets, and they had "roots" everywhere. (TV: The End of the World)
The Trees were descended from trees in the tropical rainforest on Earth. (TV: The End of the World) The Forest lived on the planets Cheem (PROSE: The Game of Death) and New Earth, where they were hunted by the Termitons before the New Earth Senate stopped them. (AUDIO: Death in the New Forest)
The Trees of Cheem were considered to be one of the higher species and were witnesses to the Last Great Time War. They were aware of the course of the war and its history-changing effects, and were horrified by the bloodshed. (PROSE: Meet the Doctor)
During the destruction of Earth in 5,000,000,000, a group of trees were on Platform One, due to the Forest of Cheem's wealth, attending the event to keep up their share prices as well as paying respects. The group of Trees seen on Platform One was led by Jabe and also included Coffa and Lute. (TV: The End of the World)
At some point after the destruction of Earth, Coffa and Lute were menaced by some unknown force who were hunting down the survivors of Platform One. When they tried to warn the Tenth Doctor and Rose Tyler, they were discovered by Montodon Slemm, who intended to capture them for resale. Though the Doctor and Rose were able to stop Montodon, Coffa and Lute were captured by the Elth of Balhoon in the confusion. (COMIC: Growing Terror) Elth held the survivors of Platform One responsible for his brother's death and planned to kill them in revenge. When the truth came out, Coffa and Lute agreed to plant a garden in remembrance. (COMIC: Reunion of Fear)
Behind the scenes
- According to Monsters and Villains, a non-narrative source, the Brothers of Hame brought a 500x300-mile plot of trees from the rainforests on Earth to the Panjassic Asteroid Field during the Middle Blue Period of Earth, where the trees' evolution was accelerated from a billion years to just three years. Collectively, the Trees of Cheem turned against their creators and fled into space in spaceships made from bark. Two hundred years after the experiments, they had chosen the name Forest of Cheem for themselves, taking the name from their word for water.