Tree of Life
The "Tree of Life" is a mythological archetype that spans many religions and cultures, including the Eternal Banyan Tree (Akshaya Vata) of Hinduism; the Bo tree of Buddhism; the Etz Chaim in Judaism, Kabbalah, and Christianity; and Yggdrasil of the Norse tradition, among many others.
After extracting the information needed from Donatello Redfield's mind for the spell to open a rift, Castiel reveals that one of the key ingredients is fruit from the Tree of Life. Castiel travels to Syria to collect the fruit; while not mentioned it can be assumed that he journeyed to the Assyrian Tree of Life found in Ancient Mesopotamia and Urartu mythology. Upon reaching the tree, Castiel finds that it is guarded by a pack of djinn. He is able to kill most of the guards, and ends up negotiating with the remaining, possibly becoming married to the djinn queen in exchange for a bag of the mangosteen-like fruit.
Fruit from the Tree of Life was used in a ceremony to bring forth the cosmic deities Yokoth and Glythur in 1925 by a rogue sect of the Men of Letters led by Diego Avila in Portsmouth, Rhode Island. The fruit was crushed in a bowl and mixed with two other ingredients: blood of a most holy man and archangel grace. With the Seal of Solomon focusing the energy, a rift was opened, allowing Yokoth entry into their universe.