Guarana (Portuguese guaraná [ɡwaɾɐˈna]), Paullinia cupana (syn. P. crysan, P. sorbilis), is a climbing plant in the Sapindaceae family, native to the Amazon basin and especially common in Brazil. Guarana features large leaves and clusters of flowers, and is best known for its fruit, which is about the size of a coffee berry. Each fruit harbors one seed which contains approximately five times as much caffeine as coffee beans. This plant, as is generally the case with caffeine, evolved such a concentration because caffeine is poisonous to and repels pests that would otherwise eat or damage the berries.
The guarana fruit's color ranges from brown to red and contains black seeds which are partly covered by white arils. The color contrast when the fruit has been split open has been likened to eyeballs; this has formed the basis of a myth.