Asclepiadaceae is a traditional and easily recognized family, which has recently been treated as subfamily (Asclepiadoideae) of Apocynaceae. This modification of the usual classification is not based on new phylogenetic hypotheses but on changes in the concept of taxonomic arrangement. The segregation of Asclepiadaceae from Apocynaceae is unsustainable in modern systematics and it is maintained only in anachronistic classifications. Phylogenetic relationships of groups included in Apocynaceae, however, are problematic and the delimitation of Asclepiadoideae is uncertain. Some Old World groups have questionable taxonomic position, but this does not affect either the recognition of the subfamily in the New World or phylogenetic studies of most American groups. In the New World, all members of Asclepiadoideae have true pollinaria and would be included in what was originally recognized as "Asclepiadeae verae", a presumably monophyletic group.