Bananas (or Cave Bananas in the base game) are FoodItems found on Cave Banana Trees. These trees grow underground and will regrow after 4 days once picked. Splumonkeys will pick Bananas from Cave Banana Trees on sight, which has no effect on the 4-day regrowth period of Bananas. Splumonkeys also are more likely to follow and steal from a player if the player is carrying any number of Bananas.
The Cave Banana is the only item in the game with examination quotes from every character other than Wes.
The raw image for the Banana shows multiple bananas in one bunch, but the Cooked image shows only three, which seem to be poorly prepared. This could hint to poor cooking/preparation due to abnormal food.
Wickerbottom's quote mentions that all of the bananas are genetically identical. This is probably a reference to the concern from botanists over the increase in cloned banana trees which could theoretically make them infertile. This could also be the reason Cave Banana Trees cannot be grown by the player.
The Cave Banana name is possibly a play on one of the most common banana cultivars, Cavendish Bananas.