Abstract
Macrosamanea macrocalyx is an endemic species from the state of Pará in Brazil. It was described based on specimens collected by A. Ducke in 1916 and J.G. Kuhlmann in 1924, in the municipality of Altamira. Since then, the species has not been recorded. The construction of the Belo Monte hydroelectric dam on the Xingu River permanently flooded a large area in this region. We report the rediscovery of M. macrocalyx in its natural habitat, and provide new taxonomic information, particularly the first description of the mature fruits and seeds. We evaluate its conservation status as critically endangered (CR), based on current knowledge and the IUCN criteria.