Oxypetalum is the largest genus of Oxypetalinae (Apocynaceae-Asclepiadoideae) and presents its highest diversity in southern South America. A new species, Oxypetalum globosum, from montane environments of northern Argentina, is described, illustrated, and compared to similar species. Data on its habitat, distribution, ecology, and phenology are provided. This is an outstanding species within Oxypetalum due to its flowers with maroon, globose corollas, with patent, rounded corolla lobes, and a bright pink, exserted, hemispheric stylar-head appendage, which suggest fly- pollination. The difficulties in delimiting genera of Oxypetalinae are discussed. A key to the species of Oxypetalum from northern Argentina is included. [ABSTRACT FROM AUTHOR]