Treeborg
From Tardis Wiki, the free Doctor Who reference
"Treeborgs" were partially organic, partially robotic trees kept aboard the Byzantium. The trees fed on starlight and gave out oxygen, which was harvested and sprayed throughout the ship. The treeborgs were also capable of giving light, and so were attacked by the Weeping Angels to plunge the vault into darkness. (DW: Flesh and Stone)
