Sauropus assimilis is an extremely rare species of plant in the Phyllanthaceae family. It is a tree growing in wet evergreen forests in lowlands. Endemic to southwestern Sri Lanka, and only known from the Sinharaja Biosphere Reserve there, evidence of its existence was last catalogued before 1991 (in a survey held between 1991–1996 by the National Conservation Review of Sri Lanka), and it has not been found since then. It may have since become extinct.