Guarana (Paulinia cupana) is a climbing plant in the maple family, Sapindaceae, native to the Amazon basin and especially common in Brazil. Guarana features large leaves and clusters of flowers, and is best known for the seeds from its fruit, which are about the size of a coffee bean. As a dietary supplement, guarana is an effective stimulant. Its seeds contain about twice the concentration of caffeine found in coffee seeds (about 2–4.5% caffeine in guarana seeds compared to 1–2% for coffee seeds).
As with other plants producing caffeine, the high concentration of caffeine is a defensive toxin that repels herbivores from the berry and its seeds.
The guarana fruit’s colour ranges from brown to red and contains black seeds which are partly covered by white arils. The colour contrast when the fruit is split open has been compared with the appearance of eyeballs, and has become the basis of an origin myth among the Sateré-Mawé people.