Background – The species diversity within the tribe Spermacoceae (Rubiaceae) remains imperfectly known. As part of an ongoing revision of South-American species of the tribe, a new species of the genus Spermacoce s. str. is here presented. Methods – Normal practices of herbarium taxonomy have been applied to study all herbarium material available. Pollen was studied using the acetolysis method. Key results – Spermacoce paganuccii E.L. Cabral & Bacigalupo a new species from Brazil is described and illustrated. The species is endemic of Serra do Orobó from the state of Bahia. Morphologically it is most similar to Spermacoce glabra and S. spiralis. It differs from S. glabra in the diameter of the glomerules, the form and indumentum of the capsules and the habit. The new species is easily distinguished from S. spiralis by its indehiscent fruits, the glomerule disposition, the number of bractal leaf and the calyx lobes. Pollen morphology is also analyzed and its relevance is discussed to distinguish the new species from its closest relatives.

BRAZIL; POLLEN MORPHOLOGY; RUBIACEAE; SPERMACOCE; SYSTEMATICS