For the Asclepiadoideae he concluded that "the border between a receptacular base of the staminal column and an upper part in which the filaments are fused cannot be made out.
In his later paper Kunze (1996: 567) stated that the filament tube in the Asclepiadoideae has evolved by "replacement of the original free filaments by new elements originating from the inward[ly] protruding base[s] of the filaments.
Another important fact is that while the situation described in the third stage leads naturally (in our view) to that in the Asclepiadoideae, the arrangement in first stage is similar to that in various Rauvolfioideae and Apocynoideae (cf.
Further aspects lend support to the existence of a cline from the Periplocoideae to the Asclepiadoideae.
This situation again bears considerable similarity to many coronas found in the Asclepiadoideae.
In the Asclepiadoideae the primary nectaries are located behind the guide rail at the top of the so-called filament tube and above the filaments.
Morphologically, the Secamonoideae fall somewhere between the Periplocoideae and the Asclepiadoideae and share characters with both of these subfamilies.
However, in the Secamonoideae with functionally bisporangiate anthers, it is the two inner (ventral) ones that are reduced (Civeyrel, 1995, 1996), whereas in the Asclepiadoideae it is the two outer (dorsal) ones that have become obsolete.
A more detailed inspection of the pollinia of the Secamonoideae shows that they differ from those in the Asclepiadoideae in that they are composed of tetrads held together by cross-wall fusion, without an outer wall enclosing the pollinium.