Molecular analyses have indicated that several Australian taxa previously identified as the red alga Plocamium cartilagineum do not group with that species as known from its northern hemisphere type locality. One of these species-level genetic groups corresponds precisely with Plocamium pusillum, a species described by Sonder in 1845 based on Preiss specimens from south-western Australia, but regarded as a heterotypic synonym of P. cartilagineum in recent morphology-based treatments. A specimen of P. pusillum in the Melbourne Herbarium (MEL) has been examined and designated as lectotype; its morphology agrees with recently collected specimens included in molecular analyses and is clearly shown to differ from authentic P. cartilagineum. Plocamium pusillum is therefore resurrected and is characterized genetically and morphologically.