The Apocynaceae Family was named and described by Antoine Laurent de Jussieu in Genera Plantarum in 1789.
All the plants I have grown or are wildflowers on the farm that were members of the Asclepiadoideae Family (the Milkweed Family) are now members of the Apocynaceae Family. The APG II system changed that and says it should be classed as a subfamily of the Apocynaceae Family. It is strange that the Huernia schneideriana and Asclepias species are in the same family and/or subfamily. Of course, there are many genera of succulents, perennials, and trees in this HUGE family… According to the Wikipedia, there are currently (as of 1-1-18) 348 genera with about 2,900 species in this subfamily alone. Plants of the World Online lists 380 genera in the Apocynaceae Family with no mention of a subfamily and says Asclepiadaceae is a synonym of Apocynaceae. Maybe other APG systems (III or IV) changed the classification and the subfamily Asclepiadaceae is no more… Well, that would be weird because the Wikipedia article was last edited on July 10, 2017. The APG II system took effect in 2003, III in 2009, and IV in 2016… The Llifle (Encyclopedia of Living Forms) still maintains the succulents in this “group” are still members of the Asclepiadoideae Family… Someday everyone will be on the same page.