Introduction

Apocynaceae, including its subfamilies, has about 4800 species and 480 genera (Struwe et al., 1994; Mabberley, 2008). Endress and Bruyns (2000) proposed a revised classification of Apocynaceae, which includes five subfamilies: Rauvolfiodeae, Apocynoideae, Periplocoideae, Secamonoideae, and Asclepiadoideae. The subfamily Asclepiadoideae was formerly known as Asclepiadaceae (Endress and Bruyns, 2000). Asclepiadoideae has 177 genera and 3,000 species (Meve, 2002) and has four tribes – Fockeeae, Asclepiadeae, Marsdenieae, and Ceropegieae (Endress and Bruyns, 2000). Asclepiadoideae has the most elaborate and complex flowers of all dicots (Endress, 1994).