Pollen morphology of the Periplocoideae, Secamonoideae, and Asclepiadoideae (Apocynaceae)

Among Apocynaceae the Periplocoideae are distinguished from the Secamonoideae and Asclepiadoideae by the presence of presences of free tetrads or pollinia, which are shed onto spoon-shaped translators after anthesis. The Secamonoideae are distinguished from Asclepiadoideae by having four pollinia attached to a translator, rather than two pollinia as in Asclepiadoideae. In the Periplocoideae the exine consists of a tectum and a granular stratum. In Secamonoideae the exine consists of three layers: an outer lectum, subtended by a well-developed granular layer, which is followed by a foot layer. In the Asclepiadoideae the exine consists of a tectum (distal exine layer), a thin granular layer, and all inner foot layer.