Acioa edulis

Acioa edulis, syn. Couepia edulis (Prance) Prance, is a fruit and timber tree in the family Chrysobalanaceae, which is native to the Amazon Rainforest in Brazil. The tree's Portuguese common name is Castanha-de-cutia. The tree grows naturally only within a small area of Brazil; however, they proliferate widely within this area. The tree is around 25 m (82 ft) tall, with entire leaves that are oval or round, measuring 8–10 cm (3.1–3.9 in) diameter, with a petiole up to 2.5 cm (0.98 in) long. Its fruit ranges from 8–9 cm (3.1–3.5 in) long and 4–5 cm (1.6–2.0 in) diameter. and contain a single nut. Later these nuts float on the waters and have been collected for centuries as the source of a valuable oil, but their source was unknown until 1978 when botanical explorer Ghillean Prance discovered the species of tree which produces them....read more on Wikipedia.