The subtribe Orthosiinae (Apocynaceae, Asclepiadoideae, Asclepiadeae) is monophyletic and comprises four genera. Monsanima Liede & Meve is herein validly established, comprising one species, M. rnorrenioides (Goyder) Liede & Meve. This new genus is sister to a clade consisting of Jobinia E. Fourn., Orthosia Decne., and Scyphostelma Baill. A taxonomic key to these four genera is provided. For Jobinia, one species, J. peruviana Liede & Meve, is newly described, and 13 species previously treated principally under Cynanchum L. are transferred, so that the genus now comprises 25 species. Jobinia fontellana Liede & Meve is proposed as a new name, replacing O. hatschbachii Fontella & Goes. The following new combinations are made in Jobinia: J. canoi (Morillo) Liede & Meve, J. formsoa (N. E. Br.) Liede & Meve, J. latipes (Decne.) Liede & Meve, J. mazzuchii (Speg.) Liede & Meve, J. samuelssonii (Malme) Liede & Meve, J. schizocorona (Liede & Meve) Liede & Meve, J. streptantha (Malme) Liede & Meve, J. tarmensis (Schltr.) Liede & Meve, J. tiarata (Malme) Liede & Meve, J. trifurcate (Griseb.) Liede & Meve, and J. umbellate (Rushy) Liede & Meve. In Orthosia, the new combination O. angustifolia (Turcz.) Liede & Meve is made. Orthosia thymifolia Schltr. is excluded from the genus and the new combination Ditassa thymifolia (Schltr.) Liede & Meve (Metastelmatinae) is proposed. The genus Scyphostelma is reinstated, and 26 species, most previously in Cynanchum, are transferred: S. beckii (Morillo) Liede & Meve, S., bifida (Liede & Meve) Liede & Meve, S. brachyphylla (K. Schum.) Liede & Meve, S. carmenaemiliae (Morino) Liede & Meve, S. chimboracensis (Morillo) Liede & Meve, S. confusa (R. W. Holm) Liede & Meve, S. ecuadorensis (Schltr.) Liede & Meve, S. filisepala (Standl.) Liede & Meve, S. harlingii (Morino) Liede & Meve, S. intri,cata(K. Schum.) Liede & Meve, S. isidrensis (Morino) Liede & Meve, S. lechleri (Morino) Liede & Meve, S. longecalicina (Morino) Liede & Meve, S. luteynii (Morillo) Liede & Meve, S. microphylla (Kunth) Liede & Meve, S. nubicola (Morino) Liede & Meve, S. pichinchensis (K. Schum.) Liede & Meve, S. ruizteranii (Morillo) Liede & Meve, S. serpyllifolia (Kunth) Liede & Meve, S. siderocalyx (Morillo) Liede & Meve, S. sodiroi (K. Schum.) Liede & Meve, S. tenella (L. f.) Liede & Meve, S. trianae (Schltr.) Liede & Meve, S. veleziae (Morillo) Liede & Meve, S. velutina (Morino) Liede & Meve, and S. wurdackii (Morino) Liede & Meve. Ten names are lectotypified: C. ecuadorense Schltr., J. formosa, J. tarmensis, J. tiarata, J. trifurcate, J. umbellate, S. brachyphylla, S. ecuadorensis, S. intricate, and S. pichinchensis. Three names are neotypified: J. chlorantha (K. Schum.) Malme, S. sodiroi, and S. trianae.