Abstract
Three small South American genera of Apocynaceae-Asclepiadoideae are included in a phylogeny of South American Apocynaceae-Asclepiadoideae using the trnT–L and trnL–F intergenic spacers and the trnL and rps16 introns. Two genera, Widgrenia and Rhyssostelma, are nested in the large genus Oxypetalum. One, Stenomeria, is congeneric with Tassadia. The correspondent and necessary new combinations, Oxypetalum nigricans and O. corymbosum, and Tassadia decalepis, T. fosteri and T. pentalepis are made. The new combination Tassadia guanchezii is proposed for a hitherto insufficiently known species of white sand savannas of Colombia and Venezuela. Lorostelma struthianthus, a synonym of Tassadia decalepis, is lectotypified. This manuscript proposes taxonomic changes that reflect advances in Oxypetalinae and Tassadiinae, and it emends the description of Tassadia guanchezii.