Apples appear in many religious traditions, often as a mystical or forbidden fruit. One of the problems identifying apples in religion, mythology and folktales is that as late as the 17th century, the word "apple" was used as a generic term for all (foreign) fruit other than berries, but including nuts. This term may even have extended to plant galls, as they were thought to be of plant origin (see oak apple). For instance, when tomatoes were introduced into Europe, they were called "love apples". In one Old English work, cucumbers are called eorþæppla (lit. "earth-apples'), just as in French, Dutch, Hebrew, Afrikaans, Persian and Swiss German as well as several other German dialects, the words for potatoes mean "earth-apples". In some languages, oranges are called "golden apples" or "Chinese apples". Datura is called "thorn-apple".
Ethnobotanical and ethnomycological scholars such as R. Gordon Wasson, Carl Ruck and Clark Heinrich write that the mythological apple is a symbolic substitution for the entheogenic Amanita muscaria (or fly agaric) mushroom. Its association with knowledge is an allusion to the revelatory states described by some shamans and users of psychedelic mushrooms. At times artists would co-opt the apple, as well as other religious symbology, whether for ironic effect or as a stock element of symbolic vocabulary. Thus, secular art as well made use of the apple as symbol of love and sexuality. It is often an attribute associated with Venus who is shown holding it.
Though the forbidden fruit in the Book of Genesis is not identified, popular Christian tradition holds that Adam and Eve ate an apple from the forbidden tree in the Garden of Eden. The unnamed fruit of Eden thus became an apple under the influence of the story of the golden apples in the Garden of Hesperides. As a result, the apple became a symbol for knowledge, immortality, temptation, the fall of man and sin. According to the Bible, there is nothing to show the forbidden fruit of the tree of knowledge was necessarily an apple.