What is the apple of eden

It represents, generally 'forbidden'.

Also look to the precursors to the Garden of Eden myth:

The Babylonian 'Epic of Gilgamesh' and the Sumerian 'paradise' named Dilmun.

Both of these tales influence much of the 'Garden of Eden' story.

The Sumerian myth details 8 plants:

"Enki desired to eat these plants and sent his messenger Isimud to fetch them. Enki ate them one by one, and Ninhursag in her rage pronounced the curse of death upon Enki..."

"...The great gods were in dismay and Enlil [the chief god] was powerless to help. Ninhursag was induced to return and deal with the situation. She created eight goddesses of healing who proceeded to heal each of the diseased parts of Enki's body. One of these parts was the god's rib, and the goddess who was created to deal with the rib was named Ninti, which means "lady of the rib"

The quest of of Gilgamesh (for immortality) was told by Utnapishtim (the Babylonian "Noah") . It states that there was a plant at the bottom of the sea that had the property of making the old young again.

Gilgamesh dived into the sea and brought up the plant. The plant was stolen by a serpent.