Abstract— A new species Strychnos dantaensis was discovered in lowland forest of Poço das Antas Biological Reserve, and is the unique tree species of the genus Strychnos in Rio de Janeiro State. The new species is related to S. trinervis
(Vell.) Mart., but differs by its arborescent growth form, absence of tendrils on branches, ovate calyx lobes, and oblong anthers. Strychnos dantaensis should be treated as endangered under IUCN red list criteria due to its restricted geographical distribution in the Atlantic Rain Forest,
an ecosystem in continuous decline.