Revision of Microgyne (Asteraceae: Astereae), the Correct Name for Microgynella

South American Microgyne Less. is resurrected from the synonymy of Microgynella. Microgyne Cass. is a nomen nudum and therefore not validly published. The replacement generic name Microgynella, a homotypic synonym of Microgyne Less., is illegitimate and superfluous. A revision is presented for the two species of Microgyne, one herein described as new. The new species, Microgyne marchesiana, is described from Uruguay and is diagnosed by pinnatifid leaves, whitish pappus, and a thick testa. A neotype is designated for Microgyne trifurcata Less. Detailed descriptions and illustrations are provided for the two species, together with additional data on anatomy.