Leef Apple Glyn Slitheen-Blathereen was a member of the Slitheen-Blathereen family and the wife of Tree. Tree and she looked down on the Blathereen side of their family and were addicted to eating Rakweed.
In 2009, Leef and Tree hatched a plan to spread the Rakweed across Earth for huge profits. They landed their ship in Antarctica and used it as a base. They gave a Rakweed plant as a gift to Sarah Jane Smith, gaining her trust by first foiling a Slitheen plan to destroy Earth and posing as bounty hunters.
The Rakweed started to infect London, including Sarah Jane's son, Luke. Enraged by this, Sarah Jane teleported herself to the ship and threatened Tree and Leef with a water gun filled with vinegar. Leef tricked Sarah Jane into lowering her guard by feigning ignorance of the Rakweed's effects; Tree falsified removal of the plant. When Sarah Jane lowered her weapon, Leef restrained her. However, Sarah Jane escaped and found a way to destroy the Rakweed and stop the infection.
Leef and Tree transported themselves to Sarah Jane's attic and tried to kill her and her friends. Sarah Jane had Mr Smith replicate the sound of an alarm bell to destroy the Rakweed in Leef and Tree's stomachs. This caused a massive methane gas build-up which killed them both. Clyde Langer called this farting themselves to death. (TV: The Gift)