Most genera of the subfamily Asclepiadoideae (i.e., 29 genera) can be found in the southeastern Brazilian region. Among these, the most representative is Oxypetalum R. Br., with 71 taxa (including specific and infraspecific). In Rio de Janeiro State, there are 25 taxa of Oxypetalum that are climbers, with the exception of O. patulum E. Fourn., which is a suberect shrub and decumbent. Most taxa from Rio de Janeiro occur in secondary Atlantic Forest, but four are from sandy coastal plain (restinga) vegetation, namely O. alpinum (Vell.) Fontella & E. A. Schwarz var. alpinum, O. pachyglossum Decne., O. banksii Schult. subsp. banksii, and O. banksii subsp. corymbiferum (E. Fourn.) Fontella & C. Valente. The latter species is restricted to restingas. Some taxa occur in high-altitude grasslands, namely O. costae Occhioni, O. lanatum Decne ex E. Fourn., O. patulum E. Fourn., O. sublanatum Malme, O. insigne (Decne.) Malme var. insigne, O. insigne var. glabrum (Decne.) Fontella & E. A. Schwarz, O. insigne var. glaziovii (E. Fourn.) Fontella & E. A. Schwarz, and O. regnellii (Malme) Malme. Four species and one subspecies are endemic to the state of Rio de Janeiro: O. costae, O. glaziovianum Loes., O. lutescens E. Fourn., O. schottii E. Fourn., and O. banksii subsp. corymbiferum. Two species are cited here as new records for the state of Rio de Janeiro: O. molle Hook. & Arn. and O. pannosum Decne. var. pannosum. The following taxa are proposed as new synonyms: O. sobralii Occhioni (= O. schottii), O. villosum E. Fourn. (= O. pachyglossum Decne.), and O. mourai Hoehne (= O. glaziovianum Loes.). Oxypetalum appendiculatum Mart., O. molle, O. pannosum var. pannosum, O. sublanatum, O. wightianum Hook. & Arn., and O. banksii subsp. banksii are widely distributed, the first five reaching Paraguay and Argentina, while O. banksii subsp. banksii is limited to Brazil (from Alagoas to Rio Grande do Sul). Lectotypifications were made for the following species: Calostigma guilleminianum Decne., Cystostemma glandulosum Silveira, Oxypetalum glaziovianum Loes., O. lanatum, O. mourai, O. pachyglossum,