Hypericum bordignonii (Hypericaceae) is a new species from Rio Grande do Sul, Brazil. This species belongs to Hypericum section Trigynobrathys, and is morphologically most similar to H. legrandii. The new species can be distinguished from all other species of the genus by having anthers with prolonged connectives, a characteristic that has never been described before for Hypericum. Moreover, the species is endemic to a single granite hill called Santa Teresa in Porto Alegre municipality, in Southern Brazil. We present here a morphological description and illustrations of H. bordignonii. We also provide information on the conservation status of the species and suggest its inclusion in the IUCN red list of threatened species as critically endangered (CR).