Clidemia fluminensis Baumgratz & D'El Rei Souza (section Staphidium (Naudin) Griseb., Melastomataceae, Miconieae), a new species from Rio de Janeiro, Brazil, is described and illustrated. The new taxon occurs in Poço das Antas Biological Reserve in alluvial forest of the Atlantic Forest ecosystem. The new species is distinguished mainly by the scandent habit, membranous leaves, terminal inflorescences, and flowers with yellow petals with an obtuse and apiculate apex. It is related to C. conglomerata DC. and C. involucrata DC., sharing the glomeruliform inflorescence, the stamen connective not prolonged or appendaged, and the pilose ovary apex.